Iron composite particles for purifying soil or ground water, process for producing the same, purifying agent containing the same, process for producing the purifying agent and method for purifying soil or ground water

ABSTRACT

Iron composite particles for purifying soil or ground water, comprise α-Fe and magnetite, and having a ratio of a diffraction intensity D 110  of (110) plane of α-Fe to a sum of a diffraction intensity D 311  of (311) plane of magnetite and the diffraction intensity D 110  (D 110 /(D 311 +D 110 )) of 0.30 to as measured from X-ray diffraction spectrum of the iron composite particles, an Al content of 0.10 to 1.50% by weight and an S content of 3500 to 7000 ppm; a process for producing the iron composite particles; a purifying agent containing the iron composite particles; a process for producing the purifying agent; and a method for purifying soil or ground water.

BACKGROUND OF THE INVENTION

The present invention relates to iron composite particles for purifyingsoil or ground water, a process for producing the iron compositeparticles, a purifying agent containing the iron composite particles, aprocess for producing the purifying agent, and a method for purifyingsoil or ground water. More particularly, the present invention relatesto iron composite particles for decomposing and insolubilizing (1)organohalogen compounds, for example, aliphatic organohalogen compoundssuch as dichloromethane, carbon tetrachloride, 1,2-dichloroethane,1,1-dichloroethane, cis-1,2-dichloroethylene, 1,1,1-trichloroethane,1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene,1,3-dichloropropene or the like, aromatic organohalogen compounds suchas dioxins, PCB or the like, (2) heavy metals such as cadmium, lead,chromium, arsenic, selenium, cyanogens or the like, which are containedin soil or ground water, in an efficient, continuous and economicalmanner; a process for producing the iron composite particle; a purifyingagent containing the iron composite particles; a process for producingthe purifying agent; and a method for purifying soil or ground waterusing the purifying agent.

The above aliphatic organohalogen compounds such as trichloroethylene,tetrachloroethylene or the like have been extensively used for cleaningin semiconductor-manufacturing factories and for degreasing metals to bemachined.

Also, waste gases, fly ashes or main ashes discharged from incinerationfurnaces for combusting municipal garbage or industrial wastes, containaromatic organohalogen compounds such as dioxins having an extremelyhigh toxicity to human bodies even in a trace amount. The “dioxins” area generic name of such compounds formed by replacing hydrogen atoms ofdibenzo-p-dioxine, dibenzofuran, etc., with chlorine atoms. The wastegases or fly ashes continuously stay around the incineration furnace, sothat the dioxins still remain in soil of surrounding regions.

Further, PCB (polychlorinated biphenyl) has been used in manyapplication as insulating oils for transformers and capacitors,plasticizers or heating medium because of high chemical and thermalstability and excellent electrical insulating property thereof. Sincethe PCB is very harmful, the production and use thereof has beenpresently prohibited. However, any effective PCB-treating method has notbeen established until now and, therefore, a large part of the PCB pastused has still been stored without treatment or disposal.

The organohalogen compounds such as aliphatic organohalogen compounds,aromatic organohalogen compounds or the like are hardly decomposable andbesides exhibit carcinogenesis as well as a strong toxicity. Therefore,there arises such a significant environmental problem that soil orground water is contaminated with these organohalogen compounds.

More specifically, upon discharge of the above organohalogen compounds,the hardly-decomposable organohalogen compounds are accumulated in soil,and the soil contaminated with the organohalogen compounds furthercauses contamination of ground water by the organohalogen compounds. Inaddition, the contaminated ground water flows out from the contaminatedsoil and spreads over the surrounding regions, so that the problem ofpollution by the organohalogen compounds is caused over wider areas.

The soil is once contaminated with the organohalogen compounds, landinvolving the soil cannot be reused and developed again. Therefore,there have been proposed various techniques or methods of purifying thesoil and ground water contaminated with the organohalogen compounds.However, since the organohalogen compounds are hardly decomposable and alarge amount of soil and ground water must be purified, any efficientand economical purifying techniques or methods have not been fullyestablished until now.

As the method of purifying soil contaminated with the organohalogencompounds, there are known a purifying method of using variouscatalysts; a method of absorbing and removing vapors of theorganohalogen compounds by utilizing a volatility thereof; a thermaldecomposition method of heat-treating excavated soil to convert the soilinto harmless one; a method of purifying the soil by microorganisms; orthe like. In addition, as to the ground water contaminated with theorganohalogen compounds, there are known a method of extracting thecontaminated ground water out of soil and converting the ground waterinto harmless one; a method of pumping the contaminated ground water andremoving the organohalogen compounds therefrom; or the like.

Among these conventional methods of purifying soil or ground watercontaminated with the organohalogen compounds, there have been proposedmany methods of purifying the soil or ground water contaminated with theorganohalogen compounds into harmless ones by mixing and contacting thesoil or ground water with a purifying agent composed of iron-basedparticles (Japanese Patent Application Laid-Open (KOKAI) Nos. 11-235577(1999), 2000-5740, 2000-334063, 2001-38341, 2001-198567, 2002-161263,2002-210452 and 2002-317202).

On the other hand, with recent increasing consciousness of environmentalprotection, the contamination of soil or ground water by heavy metals orthe like has been noticed. In particular, soil or ground watercontaminated by harmful substances including heavy metals such ascadmium, lead, chromium, arsenic, selenium, cyanogen or the like exertssignificant influences on human bodies and ecosystem. Therefore, thedevelopment of methods for purification and removal of these harmfulsubstances has also been urgently demanded.

As well known in the art, technical measures for treatment of soil orground water contaminated with harmful substances such as heavy metalsare classified into two categories, i.e., “purification techniques” and“containment”. Further, the purification techniques are classified into“in-situ purification” and “removal by excavation” in which contaminatedsoil is excavated and removed from objective lands. Furthermore, the“in-situ purification” techniques are classified into “in-situdecomposition” in which heavy metals or the like contained in thecontaminated soil or ground water, are decomposed under the ground (insitu), and “in-situ extraction” in which the contaminated soil or groundwater is extracted or excavated, and then heavy metals or the likecontained in the soil or ground water are removed therefrom.

Further, the “in-situ extraction” techniques are classified into“decomposition” in which among objective substances belonging to the“heavy metals or the like”, compounds such as cyanogen and agriculturalchemicals are thermochemically decomposed, and “separation” in whichconcentrated heavy metals, etc., are physically separated from thecontaminated soil or ground water.

On the other hand, the “containment” techniques are classified into“in-situ containment” and “containment after removal by excavation”. Thein-situ containment techniques are techniques of solidifyingcontaminated soil by mixing a solidifying agent therewith, and thenconfining the contaminated soil in situ without displacement therefrom.The techniques of containment after removal by excavation are techniquesof pre-mixing an insolubilizing agent with contaminated soil to convertthe soil into hardly-soluble one, drilling the contaminated soil once,and then confining the contaminated soil in place.

As the working methods for executing the “purification techniques”,there may be used a soil-washing method, a heat-desorption method or thelike. For example, there may be used a chemical dissolution method inwhich chemicals are added to the contaminated soil to dissolve heavymetals or the like therein, and then the resultant solution is separatedtherefrom; a water-washing method of washing the contaminated soil withwater and then classifying the soil to separate fine particlescontaining a large amount of heavy metals or the like therefrom; a soilwet-washing method of washing out contaminants adhered onto the surfaceof soil particles with a washing agent, and further classifying the soilparticles into clean large particles and fine contaminant particlesaccording to particle size and specific gravity thereof; or the like.

Also, in the “containment” techniques, as the working method for the“in-situ containment”, there is known a method of mixing a solidifyingagent such as cement with the contaminated soil and then confining thesolidified soil by a water-impermeable layer, steel sheet pile, etc. Asthe working method for the “containment after removal by excavation”,there is known a method of adding chemicals to the contaminated soil toinsolubilize the soil and change the soil into hardly-elutable form, andthen confining the hardly-elutable soil by insulating method orwater-shielding method.

However, the above conventional treatment techniques undergo hightreating costs, and require a prolonged treating time. Therefore, thesetechniques may fail to reduce harmful substances such as heavy metals orthe like in an efficient and continuous manner.

In recent years, there have been developed low-cost treating techniquesof reducing a valence of the heavy metals mainly on the basis of areducing activity of iron particles in order to convert the heavy metalsinto harmless and stabilized form. For example, in Japanese PatentApplication Laid-Open (KOKAI) No. 2001-198567, there is described themethod of utilizing a reducing activity of iron particles to chromium(reduction in metal valence). In addition, in Japanese PatentPublication (KOKOKU) No. 52-45665 (1977), it is described that when ironparticles are added to a heavy metal ion-containing solution whose pHvalue is adjusted to about 5 to 6, and then the resultant mixture isstirred, a part of the iron particles are dissolved and precipitated inthe form of ferric hydroxide which is then transformed into goethite orlepidocrocite with increase of the pH value, whereupon a part of theheavy metals are co-precipitated together with the goethite orlepidocrocite, so that a large part of the heavy metals are adsorbedinto the resultant iron particles. Also, it is described that the amountof the iron particles eluted is increased at a low pH value, resultingin deteriorated adsorption/removal effect thereof.

In Japanese Patent Application Laid-Open (KOKAI) No. 11-235577 (1999),there is described a method of adding and mixing in soil, iron particlescontaining carbon in an amount of not less than 0.1% by weight toconvert organohalogen compounds contained in the soil into harmlessones. In this method, although the specific surface area and particlesize of the iron particles used are specified, since the particle sizeis too large, it may be difficult to fully decompose the organohalogencompounds.

In Japanese Patent Application Laid-Open (KOKAI) No. 2000-5740, there isdescribed the method of converting organohalogen compounds contained insoil into harmless ones using copper-containing iron particles. However,since decomposition of the organohalogen compounds requires a longperiod of time, this method may also fail to efficiently convert theorganohalogen compounds into harmless ones.

In Japanese Patent Application Laid-Open (KOKAI) No. 2000-334063, thereis described the method of contacting dioxins with an aqueoushydrochloric acid solution containing mill scale produced from theproduction process of hot-rolled steel plate in ironworks, at atemperature lower than 100° C. to convert the dioxins into harmlessones. However, since the use of the aqueous hydrochloric acid-solutionis essentially required in order to promote conversion of theorganohalogen compounds into harmless ones, the decomposition reactionof the mill scale by itself may fail to proceed sufficiently.

In Japanese Patent Application Laid-Open (KOKAI) No. 2001-38341, thereis described a soil-purifying agent composed of a water suspensioncontaining iron particles having an average particle diameter of 1 to500 μm. However, since the iron particles used have a too large particlesize, it may be difficult to fully decompose the organohalogencompounds.

In Japanese Patent Application Laid-Open (KOKAI) No. 2001-198567, thereis described the method of using a water suspension containing sphericaliron particles having an average particle diameter of less than 10 μm.Since the water suspension containing the spherical iron particles isobtained by collecting dusts contained in waste gas discharged duringrefining process from an oxygen blowing converter for steel-making, andremoving gases from the dusts, it may be difficult to fully reduce theorganohalogen compounds.

Further, the above method described in Japanese Patent ApplicationLaid-Open (KOKAI) No. 2001-198567 is the method of converting theharmful substances into harmless and stabilized ones by utilizing thereducing activity of the iron particles (reduction in valence). However,the iron particles suffer from deterioration in the reducing activitywith the elapse of years, thereby failing to continuously maintain thereducing activity. As a result, even though the heavy metals aretemporarily converted into those having a stable and harmless lowvalence, there is a possibility that the valence is thereof increasedagain, so that the heavy metals are converted into previous harmlessones. Therefore, the above method fails to provide a long-term effectivepurification method.

In Japanese Patent Application Laid-Open (KOKAI) No. 2002-161263, thereare described iron particles for decomposing organohalogen compounds inwhich a part of the surface of the iron particles is adhered with ametal selected from nickel, copper, cobalt and molybdenum, and theremaining part of the surface other than the surface adhered with theabove metal is covered with an iron oxide film. However, the ironparticles used are iron particles obtained from mill scale or ironparticles obtained by atomizing molten steel with water. As is apparentfrom the specific surface area of the iron particles as describedtherein, it is considered that the iron particles have a large particlesize. Thus, the iron particles may also fail to fully reduce theorganohalogen compounds.

In Japanese Patent Application Laid-Open (KOKAI) No. 2002-210452, it isdescribed to use sulfur-containing iron particles for purificationtreatment of soil or ground water contaminated with organohalogencompounds. However, since the iron particles have a too large particlesize, it may be difficult to fully reduce the organohalogen compounds.

Also, in Japanese Patent Application Laid-Open (KOKAI) No. 2002-317202,it is described to use magnetite-containing iron composite particles forpurification treatment of soil or ground water contaminated withorganohalogen compounds. However, since the iron particles contain nosulfur, it may be difficult to fully reduce the organohalogen compounds.

In addition, the method described in Japanese Patent Publication(KOKOKU) No. 52-45665 (1977) utilizes mainly the reducing activity orabsorption activity of the iron particles. Although these activities areattained by a partial dissolution of the iron particles, the method isbased on such a mechanism that when the iron particles are eluted over awhole acidic range and then converted into goethite, lepidocrocite ormagnetite, the heavy metals are included therein. Therefore, this methodis not a method of positively using such a phenomenon that the ironparticles are dissolved in the form of Fe²⁺ or Fe³⁺ and formed intospinel ferrite while incorporating heavy metals therein.

As a result of the present inventors' earnest studies for solving theabove problems, it has been found that resultant iron compositeparticles obtained by cooling iron particles obtained by heat-reducinggoethite or hematite particles having a specific average particlediameter and a specific Al content at a temperature of 350 to 600° C.;transferring the obtained iron particles into water without forming asurface oxidation film on surface of the iron particles in a gas phase;forming the surface oxidation film on the surface of the iron particlesin water; and then drying the iron particles provided with the surfaceoxidation film, are capable of treating organohalogen compounds and/orheavy metals contained in the soil or ground water in an efficient,continuous and economical manner. The present invention has beenattained on the basis of this finding.

SUMMARY OF THE INVENTION

An object of the present invention is to provide iron compositeparticles for purifying soil or ground water, which are capable oftreating organohalogen compounds and/or heavy metals contained thereinin an efficient, continuous and economical manner, as well as a processfor producing the iron composite particles.

Another object of the present invention is to provide a purifying agentfor soil or ground water, which are capable of treating organohalogencompounds and/or heavy metals contained therein in an efficient,continuous and economical manner, as well as a process for producing thepurifying agent.

A further object of the present invention is to provide a method forpurifying soil or ground water by treating organohalogen compoundsand/or heavy metals contained therein.

To accomplish the aims, in a first aspect of the present invention,there is provided iron composite particles for purifying soil or groundwater, comprising α-Fe and magnetite, and having a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₀ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.30 to 0.95 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of 0.10 to 1.50% by weight and an S content of3500 to 7000 ppm.

In a second aspect of the present invention, there is provided ironcomposite particles for purifying soil or ground water, comprising α-Feand magnetite, and having a ratio of a diffraction intensity D₁₁₀ of(110) plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311)plane of magnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀))of 0.30 to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.10 to 1.50% by weight, an Scontent of 3500 to 7000 ppm, a saturation magnetization value of 85 to155 μm²/kg, a BET specific surface area of 5 to 60 m²/g, a crystallitesize of (110) plane of α-Fe of 200 to 400 Å, and an average particlediameter of 0.05 to 0.50 μm.

In a third aspect of the present invention, there is provided ironcomposite particles for purifying soil or ground water, comprising α-Feand magnetite, and having a ratio of a diffraction intensity D₁₁₀ of(110) plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311)plane of magnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀))of 0.32 to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.20 to 1.20% by weight, an Scontent of 3800 to 7000 ppm, a saturation magnetization value of 90 to155 Am²/kg, a BET specific surface area of 7 to 55 m²/g, a crystallitesize of (110) plane of α-Fe of 200 to 350 Å, and an average particlediameter of 0.05 to 0.30 μm.

In a fourth aspect of the present invention, there is provided a processfor producing iron composite particles for purifying soil or groundwater, comprising:

heat-reducing goethite particles having an average major axis diameterof 0.05 to 0.50 μm, an Al content of 0.06 to 1.00% by weight and an Scontent of 2200 to 4500 ppm or hematite particles having an averagemajor axis diameter of 0.05 to 0.50 μm, an Al content of 0.07 to 1.13%by weight and an S content of 2400 to 5000 ppm, at a temperature of 350to 600° C. to produce iron particles;

after cooling, transferring the iron particles into water withoutforming a surface oxidation film on surface of the iron particles in agas phase;

forming the surface oxidation film on the surface of the iron particlesin water; and

then drying the iron particles having the surface oxidation filmthereon.

In a fifth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining as an effective ingredient, iron composite particles whichcomprise α-Fe and magnetite, and have a ratio of a diffraction intensityD₁₁₀ of (110) plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of(311) plane of magnetite and the diffraction intensity D₁₁₀(D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20 to 0.95 as measured from X-ray diffractionspectrum of the iron composite particles, an Al content of 0.10 to 1.50%by weight, an S content of 3500 to 7000 ppm, an average particlediameter of 0.05 to 0.5 μm and a particle diameter of coarse particlesof usually 0.5 to 5.0 μm.

In a sixth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining as an effective ingredient, iron composite particles whichcomprise α-Fe and magnetite, and have a ratio of a diffraction intensityD₁₁₀ of (110) plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of(311) plane of magnetite and the diffraction intensity D₁₁₀(D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20 to 0.95 as measured from X-ray diffractionspectrum of the iron composite particles, an Al content of 0.10 to 1.50%by weight, an S content of 3500 to 7000 ppm, an average particlediameter of 0.05 to 0.5 μm and a particle diameter of coarse particlesof usually 0.5 to 5.0 μm, a saturation magnetization value of 70 to 155μm²/kg, a crystallite size of (110) plane of α-Fe of 200 to 400 Å, andan Fe content of usually not less than 65% by weight based on the weightof whole particles.

In a seventh aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining as an effective ingredient, iron composite particles whichhave a ratio of a diffraction intensity D₁₁₀ of (110) plane of α-Fe to asum of a diffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.30 to 0.95 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of 0.10 to 1.50% by weight, an S content of3500 to 7000 ppm, an average particle diameter of 0.05 to 0.50 μm, aparticle diameter of coarse particles of usually 0.5 to 3.0 μm, asaturation magnetization value of 85 to 155 μm²/kg, a crystallite sizeof (110) plane of α-Fe of 200 to 400 Å, and an Fe content of usually notless than 75% by weight based on the weight of whole particles.

In an eighth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining as an effective ingredient, iron composite particles having aratio of a diffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum ofa diffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20 to as measuredfrom X-ray diffraction spectrum of the iron composite particles, an Alcontent of 0.10 to 1.50% by weight, an S content of 3500 to 7000 ppm, anaverage particle diameter of 0.1 to 0.50 μm, a particle diameter ofcoarse particles of usually 0.5 to 4.0 μm, a saturation magnetizationvalue of 70 to 140 μm²/kg, a crystallite size of (110) plane of α-Fe of200 to 400 Å, and an Fe content of usually not less than 65% by weightbased on the weight of whole particles.

In a ninth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining iron composite particles as an effective ingredient andsodium polyacrylate, said iron composite particles comprising α-Fe andmagnetite, and having a ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311) plane ofmagnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.10 to 1.50% by weight, an Scontent of 3500 to 7000 ppm and an average particle diameter of 0.05 to0.50 μm, and a particle diameter of coarse particles of usually 0.5 to5.0 μm.

In a tenth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining iron composite particles as an effective ingredient andsodium polyacrylate, said iron composite particles comprising α-Fe andmagnetite, and having a ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311) plane ofmagnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.10 to 1.50% by weight, an Scontent of 3500 to 7000 ppm and an average particle diameter of 0.05 to0.50 μm, and a particle diameter of coarse particles of usually 0.5 to5.0 μm, a saturation magnetization value of 70 to 155 μm²/kg, acrystallite size of (110) plane of α-Fe of 200 to 400 Å, and an Fecontent of usually not less than 65% by weight based on the weight ofwhole particles.

In an eleventh aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining iron composite particles as an effective ingredient andsodium polyacrylate, said iron composite particles comprising α-Fe andmagnetite, and having a ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁, of (311) plane ofmagnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.30to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.10 to 1.50% by weight, an Scontent of 3500 to 7000 ppm, an average particle diameter of 0.05 to0.50 μm, a particle diameter of coarse particles of usually 0.5 to 3.0μm, a saturation magnetization value of 85 to 155 μm²/kg, a crystallitesize of (110) plane of α-Fe of 200 to 400 Å, and an Fe content ofusually not less than 75% by weight based on the weight of wholeparticles.

In a twelfth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining iron composite particles as an effective ingredient andsodium polyacrylate, said iron composite particles comprising α-Fe andmagnetite and having a ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311) plane ofmagnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.10 to 1.50% by weight, an Scontent of 3500 to 7000 ppm, an average particle diameter of 0.1 to 0.30μm, a particle diameter of coarse particles of 0.50 to 3.0 μm, asaturation magnetization value of 70 to 140 μm²/kg, a crystallite sizeof (110) plane of α-Fe of 200 to 400 Å and an Fe content of usually notless than 65% by weight based on the weight of whole particles.

In a thirteenth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining iron composite particles as an effective ingredient whichcomprise α-Fe and magnetite and have a ratio of a diffraction intensityD₁₁₀ of (110) plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of(311) plane of magnetite and the diffraction intensity D₁₁₀(D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20 to 0.95 as measured from X-ray diffractionspectrum of the iron composite particles, an Al content of 0.10 to 1.50%by weight, an S content of 3500 to 7000 ppm, an average particlediameter of 0.05 to 0.50 μm and, a particle diameter of coarse particlesof usually 0.50 to 5.0 μm, said iron composite particles in the watersuspension being diluted to a concentration of 0.1 to 200 g/L.

In a fourteenth aspect of the present invention, there is provided apurifying agent for soil or ground water, comprising a water suspensioncontaining iron composite particles as an effective ingredient, andsodium hydrogen carbonate, sodium sulfate or a mixture thereof, saidiron composite particles comprising α-Fe and magnetite and having aratio of a diffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum ofa diffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20 to 0.95 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of 0.10 to 1.56% by weight, an S content of3500 to 7000 ppm and an average particle diameter of 0.05 to 0.5 μm, aparticle diameter of coarse particles of usually 0.50 to 5.0 μm, asaturation magnetization value of 70 to 155 μm²/kg, a crystallite sizeof (110) plane of α-Fe of 200 to 400 Å, and an Fe content of usually notless than 65% by weight based on the weight of whole particles, saidiron composite particles in the water suspension being diluted to aconcentration of 0.1 to 200 g/L.

In a fifteenth aspect of the present invention, there is provided aprocess for producing a purifying agent for soil or ground water,comprising:

preparing a water suspension containing iron composite particles whichare produced by the steps of:

heat-reducing goethite particles having an average major axis diameterof 0.05 to 0.50 μm, an Al content of 0.06 to 1.00% by weight and an Scontent of 2200 to 4500 ppm or hematite particles having an averagemajor axis diameter of 0.05 to 0.50 μm, an Al content of 0.07 to 1.13%by weight and an S content of 2400 to 5000 ppm, at a temperature of 350to 600° C. to produce iron particles;

after cooling, transferring the iron particles into water withoutforming a surface oxidation film on surface of the iron particles in agas phase;

forming the surface oxidation film on the surface of the iron particlesin water.

In a sixteenth aspect of the present invention, there is provided amethod for purifying soil or ground water, comprising:

mixing and contacting (1) iron composite particles or (2) a watersuspension containing the iron composite particles as an effectiveingredient, with soil contaminated with organohalogen compounds and/orheavy metals or the like, or ground water contaminated withorganohalogen compounds and/or heavy metals or the like, the ironcomposite particles comprising α-Fe and magnetite, and having a ratio ofa diffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.30 to 0.95 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of 0.10 to 1.50% by weight, and an S content of3500 to 7000 ppm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between a reaction time and aresidual percentage of trichloroethylene upon purification treatment ofthe trichloroethylene using iron composite particles obtained in Example1 in which the mark “•” represents data of the iron composite obtainedin Example 1.

FIG. 2 is a graph showing a logarithmic value of a ratio of residualconcentration to initial concentration of trichloroethylene with respectto a reaction time upon purification treatment of the trichloroethyleneusing iron composite particles obtained in Example 1 in which the mark“•” represents data of the iron composite obtained in Example 1.

FIG. 3 is a graph showing arsenic, chromium and lead concentrations withrespect to a reaction time upon preparation of a sample for measurementof heavy metals as well as upon evaluation for insolubilization reaction(measurement of apparent reaction rate constant) using iron compositeparticles obtained in Example 1.

FIG. 4 is a graph showing logarithmic values of arsenic, chromium andlead concentrations with respect to a reaction time upon preparation ofa sample for measurement of heavy metals as well as upon evaluation forinsolubilization reaction (measurement of apparent reaction rateconstant) using iron composite particles obtained in Example 1.

FIG. 5 is a graph showing pH values of arsenic, chromium and leadsolutions with respect to a reaction time upon preparation of a samplefor measurement of heavy metals as well as upon evaluation forinsolubilization reaction (measurement of apparent reaction rateconstant) using iron composite particles obtained in Example 1.

FIG. 6 is a scanning electron micrograph (magnification: ×30000) showingcoarse particles produced in a purifying agent after preservation for 7months.

FIG. 7 is a graph showing a particle size distribution of a glass columnhaving a diameter of 3 cm and a length of 50 cm, used in “PenetrabilityTest”.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below. First, the ironcomposite particles for purifying soil or ground water according to thepresent invention (hereinafter referred to merely as “iron compositeparticles for purification”) are described.

The iron composite particles for purification of the present inventionis composed of an α-Fe phase and a Fe₃O₄ phase. The Fe₃O₄ content isadjusted such that the ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311) plane ofFe₃O₄ and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) is usually0.30 to 0.95, preferably 0.32 to 0.95 as measured from X-ray diffractionspectrum of the iron composite particles. When the intensity ratio(D₁₁₀/(D₃₁₁+D₁₁₀)) of the iron composite particles immediately afterproduction thereof is less than 0.30, the iron composite particles forpurification tend to be insufficient in purification performance becauseof too low α-Fe phase content therein, thereby failing to attain theaimed effects of the present invention. When the intensity ratio(D₁₁₀/(D₃₁₁+D₁₁₀)) is more than 0.95, although a sufficient amount ofthe α-Fe phase is present, the content of the Fe₃O₄ phase producedaccording to the present invention is lowered, so that the ironcomposite particles for purification tend to be early deteriorated incatalytic activity, and it is not possible to maintain a good catalyticactivity thereof for a long period of time, thereby also failing toattain the aimed effects of the present invention. In addition, Fe₃O₄ ispreferably present on the surface of the iron composite particles forpurification.

The S content of the iron composite particles for purification accordingto the present invention is usually to 7000 ppm, preferably 3800 to 7000ppm, more preferably 3800 to 6500 ppm. When the S content is less thanppm, the obtained iron composite particles for purification tend to beinsufficient in purification performance for the organohalogencompounds, thereby failing to attain the aimed effects of the presentinvention. When the S content is more than 7000 ppm, although theobtained iron composite particles for purification show a sufficientpurification performance for the organohalogen compounds, thepurification effect due to the S content is already saturated, and theuse of such a large S content is, therefore, uneconomical.

The Al content of the iron composite particles for purificationaccording to the present invention is usually to 1.50% by weight,preferably 0.20 to 1.20% by weight. When the Al content is less than0.10% by weight, the obtained iron composite particles for purificationtend to provide a hard granulated product due to volume shrinkagethereof, so that wet pulverization thereof tends to be difficult. Whenthe Al content is more than 1.50% by weight, the reduction reactiontends to proceed too slowly and, therefore, require a long period oftime. In addition, since crystal growth of the iron composite particlesfor purification is insufficient, the α-Fe phase contained therein tendsto become unstable, and a too thick oxidation film tends to be formed onthe surface of the particles.

Further, since the phase change from the Fe₃O₄ phase to the α-Fe phaseis insufficient upon the heat reduction reaction, it may be difficult toenhance the α-Fe phase content, thereby failing to attain the aimedeffects of the present invention.

The purifying iron particles of the present invention preferably have agranular shape. In the process of the present invention, since thespindle-shaped or acicular goethite or hematite particles are directlysubjected to heat reduction treatment, the particles undergo breakage ofparticle shape upon transformation into the α-Fe phase crystals, and areformed into a granular shape through isotropic crystal growth thereof.On the contrary, spherical particles have a smaller BET specific surfacearea than granular particles if the particle sizes thereof are identicaland, therefore, exhibit a less catalytic activity than that of thegranular particles. Therefore, the iron composite particles forpurification preferably contain no spherical particles.

The iron composite particles for purification of the present inventionhave an average particle diameter of usually 0.05 to 0.50 μm, preferably0.05 to 0.30 μm. When the average particle diameter of the ironcomposite particles for purification is less than 0.05 μm, the α-Fephase tends to become unstable, resulting in formation of a thickoxidation film on the surface thereof, so that it may be difficult toincrease the α-Fe phase content and attain the aimed effects of thepresent invention. When the average particle diameter of the ironcomposite particles for purification immediately after productionthereof is more than 0.50 μm, although the α-Fe phase content isincreased, the Fe₃O₄ phase content is relatively lowered, so that theiron composite particles for purification tend to be early deterioratedin catalytic activity, and it is not possible to maintain a goodcatalytic activity thereof for a long period of time. As a result, itmay be difficult to retain the Fe₃O₄ phase content to such an extentcapable of attaining the aimed effects of the present invention.

The crystallite size of (110) plane of α-Fe of the iron compositeparticles for purification according to the present invention is usually200 to 400 Å, preferably 200 to 350 Å. When the crystallite size is lessthan 200 Å, it may be difficult to increase the α-Fe phase content,thereby failing to attain the aimed effects of the present invention.When the crystallite size is more than 400 Å, although the α-Fe phasecontent is increased, it may be difficult to retain the Fe₃O₄ phasecontent to such an extent capable of attaining the aimed effects of thepresent invention.

The BET specific surface area value of the iron composite particles forpurification according to the present invention is usually 5 to 60 m²/g,preferably 7 to 55 m²/g. When the BET specific surface area value isless than 5.0 m²/g, the contact area of the iron composite particles forpurification tends to be decreased, thereby failing to show a sufficientcatalytic activity. When the BET specific surface area value is morethan 60 m²/g, it may be difficult to increase the α-Fe phase content,thereby failing to attain the aimed effects of the present invention.

The iron composite particles for purification of the present inventionhave an Fe content of usually not less than 75% by weight, preferably 75to 98% by weight based on the weight of the whole particles. When the Fecontent is less than 75% by weight, the iron composite particles forpurification tend to be deteriorated in catalytic activity, so that itmay be difficult to attain the aimed effects of the present invention.

The iron composite particles for purification of the present inventionpreferably contain substantially no metal elements other than Fe such asPb, Cd, As, Hg, Sn, Sb, Ba, Zn, Cr, Nb, Co, Bi, etc., since these metalelements exhibit a toxicity. In particular, in the consideration of highpurity and catalyst performance, the iron composite particles forpurification of the present invention preferably have a cadmium (Cd)elution of not more than 0.01 mg/L; no detected elution of wholecyanogen; a lead (Pb) elution of not more than 0.01 mg/L; a chromium(Cr) elution of not more than 0.05 mg/L; an arsenic (As) elution of notmore than 0.01 mg/L; a whole mercury (Hg) elution of not more than0.0005 mg/L; a selenium (Se) elution of not more than 0.01 mg/L; afluorine (F) elution of not more than 0.8 mg/L; and a boron (B) elutionof not more than 1 mg/L.

Also, the iron composite particles for purification of the presentinvention preferably have a cadmium and cadmium compound content of notmore than 150 mg/kg; a cyanogen compound content of not more than 50mg/kg; a lead and lead compound content of not more than 150 mg/kg; achromium (IV) compound content of not more than 250 mg/kg; an arsenicand arsenic compound content of not more than 150 mg/kg; a mercury andmercury compound content of not more than 15 mg/kg; a selenium andselenium compound content of not more than 150 mg/kg; a fluorine andfluorine compound content of not more than 4000 mg/kg; and a boron andboron compound content of not more than 4000 mg/kg.

The iron composite particles for purification of the present inventionhave a saturation magnetization value of usually 85 to 155 μm²/kg (85 to155 emu/g), preferably 90 to 155 μm²/kg (90 to 155 emu/g). When thesaturation magnetization value is less than 85 μm²/kg, the α-Fe phasecontent of the iron composite particles for purification tends to belowered, thereby failing to attain the aimed effects of the presentinvention. When the saturation magnetization value is more than 155μm²/kg, although the α-Fe phase content is increased, it may bedifficult to maintain the content of the Fe₃O₄ phase produced accordingto the present invention to such an extent capable of attaining theaimed effects of the present invention. As a result, since the Fe₃O₄phase content is relatively lowered, the iron composite particles forpurification tend to be early deteriorated in catalytic activity, and itis not possible to maintain a good catalytic activity thereof for a longperiod of time, thereby failing to readily accomplish the aims of thepresent invention.

Meanwhile, the iron composite particles for purification may be in theform of a granulated product.

Next, the purifying agent for purifying soil or ground watercontaminated with organohalogen compounds (hereinafter referred tomerely as “purifying agent”), is described.

The purifying agent of the present invention is in the form of a watersuspension containing the above iron composite particles forpurification as an effective ingredient. The content of the ironcomposite particles for purification in the water suspension may beappropriately selected from the range of usually 0.5 to 50 parts byweight, preferably 1 to 30 parts by weight based on 100 parts by weightof the water suspension.

When the content of the iron composite particles is more than 50 partsby weight, the viscosity of the purifying agent tends to be increased,thereby failing to smoothly transmit mechanical load or force uponstirring through the purifying agent and, therefore, uniformly mix thepurifying agent. As a result, it may be difficult to control theconcentration of the purifying agent.

When the particle size distribution of the iron composite particlesconstituting the purifying agent of the present invention is measured bya laser diffractometer, secondary particles of the iron compositeparticles preferably exhibit a particle size distribution with a singlepeak. When the particle size distribution of the secondary particlesexhibits a plurality of peaks, the penetration velocity of the purifyingagent into contaminated soil tends to become non-uniform, resulting inprolonged purification time, so that it may be difficult to attain theaimed effects of the present invention.

The secondary particles of the iron composite particles constituting thepurifying agent of the present invention have a median diameter D₅₀(particle diameter corresponding to an accumulative volume of particlesof 50% as measured and accumulated with respect to respective particlediameters and expressed by percentage based on a total volume of theiron composite particles as 100%) of usually 0.5 to 5.0 μm, preferably0.5 to 3.5 μm. Although the median diameter D₅₀ of the secondaryparticles is preferably as fine as possible, since the primary particlesbecome finer particles and contain α-Fe, the resultant iron compositeparticles tend to be magnetically agglomerated. Also, it may bedifficult to industrially produce such particles having a mediandiameter of less than 0.5 μm. When the median diameter of the secondaryparticles is more than 5.0 μm, the penetration into contaminated soil istoo slow, so that it may be difficult to purify the soil for a shortperiod of time, and attain the aimed effects of the present invention.

The secondary particles of the iron composite particles constituting thepurifying agent of the present invention have a ratio of D₉₀ (particlediameter corresponding to an accumulative volume of particles of 90% asmeasured and accumulated with respect to respective particle diametersand expressed by percentage based on a total volume of the ironcomposite particles as 100%) to D₁₀ (particle diameter corresponding toan accumulative volume of particles of 10% as measured and accumulatedwith respect to respective particle diameters and expressed bypercentage based on a total volume of the iron composite particles as100%) (D₉₀/D₁₀) of usually 1.0 to 5.0, preferably 1.0 to 3.5. Althoughthe ratio (D₉₀/D₁₀) is preferably as small as possible since thepenetration velocity into contaminated soil is equalized and thepurification velocity also becomes uniform, the lower limit thereof is1.0 from industrial viewpoints. When the ratio (D₉₀/D₁₀) is more than5.0, the penetration velocity into contaminated soil tends to becomenon-uniform, resulting in poor purification performance and prolongedpurification time, so that it may be difficult to attain the aimedeffects of the present invention.

The secondary particles of the iron composite particles contained in thepurifying agent of the present invention have a distribution widthD₈₄-D₁₆ (wherein D₈₄ represents a particle diameter corresponding to anaccumulative volume of particles of 84% as measured and accumulated withrespect to respective particle diameters and expressed by percentagebased on a total volume of the iron composite particles as 100%, and D₁₆represents a particle diameter corresponding to an accumulative volumeof particles of 16% as measured and accumulated with respect torespective particle diameters and expressed by percentage based on atotal volume of the iron composite particles as 100%) of usually 0.5 to5.0 μm, preferably 0.5 to 3.5 μm. Although the distribution widthD₈₄-D₁₆ is preferably as small as possible since the penetrationvelocity into contaminated soil is equalized and, therefore, thepurification velocity also becomes uniform, the lower limit thereof is0.5 μm from industrial viewpoints. When the distribution width D₈₄-D₁₆is more than 5.0 μm, the penetration velocity into contaminated soiltends to become non-uniform, resulting in poor purification performanceand prolonged purification time, so that it may be difficult to attainthe aimed effects of the present invention.

The specific gravity of the purifying agent according to the presentinvention is usually 1.2 to 1.4. When the specific gravity is less than1.2, the purifying agent tends to be uneconomical owing to a less solidcontent therein in the consideration of transportation and amount addedto soil, etc. When the specific gravity is more than 1.4, the purifyingagent has a too high viscosity in view of diameters of the primary andsecondary particles contained therein and, therefore, may be difficultto industrially produce.

Meanwhile, the iron composite particles constituting the purifying agenttend to be formed into coarse particles during the preservation periodof the purifying agent (hereinafter referred to as the “purifying agentafter preservation”). The reason therefor is considered to be that ironpresent in the vicinity of the surface of the respective particles isoxidized so that the growth of oxidation film is caused. Namely, whenthe purifying agent is preserved for a long period of time, the Fecontent in the iron composite particles is reduced and the magnetitecontent therein is increased. Notwithstanding the presence of the coarseparticles, the iron composite particles can still maintain a goodpurification performance for the organohalogen compounds and/or heavymetals or the like.

In the present invention, the presence of the coarse particles isdetermined by measuring a maximum particle diameter of the ironcomposite particles recognized from a scanning electron micrographthereof as mentioned below. The particle diameter of the coarseparticles present in the iron composite particles is usually not morethan 5.0 μm, preferably not more than 4.0 μm, more preferably not morethan 3.5 μm. When the coarse particles contained in the iron compositeparticles have a particle diameter of more than 5.0 μm, the penetrationof the purifying agent into contaminated soil tends to become extremelyslow, so that it may be difficult to purify the contaminated soil for ashort period of time, thereby failing to attain the aimed effects of thepresent invention.

The above purifying agent has the following properties

(1) The iron composite particles contained in the purifying agentaccording to the present invention are composed of α-Fe and magnetite,and have a ratio of a diffraction intensity D₁₁₀ of (110) plane of α-Feto a sum of a diffraction intensity D₃₁₁ of (311) plane of magnetite andthe diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to0.95 as measured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.5 μm, a particle diameter of coarse particles ofusually 0.5 to 5.0 μm, a saturation magnetization value of usually 70 to155 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 200 to400 Å, and an Fe content of usually not less than 65% by weight based onthe weight of whole particles.

(2) The iron composite particles contained in the purifying agent whichis preserved for a period of, for example, less than one month, arecomposed of α-Fe and magnetite, and have a ratio of a diffractionintensity D₁₁₀ of (110) plane of α-Fe to a sum of a diffractionintensity D₃₁₁ of (311) plane of magnetite and the diffraction intensityD₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.30 to 0.95, preferably 0.32 to 0.95as measured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, preferably0.20 to 1.20% by weight, an S content of usually 3500 to 7000 ppm,preferably 3800 to 6500 ppm, an average particle diameter of usually0.05 to 0.50 μm, preferably 0.05 to 0.30 μm, a saturation magnetizationvalue of usually 85 to 155 μm²/kg, preferably 90 to 155 Am²/kg, acrystallite size of (110) plane of α-Fe of usually 200 to 400 Å,preferably 200 to 350 Å, and an Fe content of usually not less than 75%by weight, preferably 75 to 98% by weight based on the weight of wholeparticles.

(3) The iron composite particles contained in the purifying agent whichis preserved for a period of not less than one month and less than 3months, are also composed of α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.5 to 0.80 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.50 μm, a particle diameter of coarse particles ofusually 0.10 to 0.60 μm, a saturation magnetization value of usually 100to 140 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 250to 400 Å, and an Fe content of usually 70 to 80% by weight based on theweight of whole particles.

(4) The iron composite particles contained in the purifying agent whichis preserved for a period of not less than 3 months and less than 6months, are also composed of α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.30 to 0.50 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.50 μm, a particle diameter of coarse particles ofusually 0.30 to 1.00 μm, a saturation magnetization value of usually 90to 100 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 250to 400 Å, and an Fe content of usually 70 to 80% by weight based on theweight of whole particles.

(5) The iron composite particles contained in the purifying agent whichis preserved for a period of not less than 6 months and less than 12months, are also composed of α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to 0.30 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.50 μm, a particle diameter of coarse particles ofusually 0.60 to 5.00 μm, a saturation magnetization value of usually 70to 90 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 250to 400 Å, and an Fe content of usually 70 to 80% by weight based on theweight of whole particles.

(6) The iron composite particles contained in the purifying agent whichis preserved for a period of not less than twelve months, are alsocomposed of α-Fe and magnetite, and have a ratio of a diffractionintensity D₁₁₀ of (110) plane of α-Fe to a sum of a diffractionintensity D₃₁, of (311) plane of magnetite and the diffraction intensityD₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to 0.30 as measured from X-raydiffraction spectrum of the iron composite particles, an Al content ofusually 0.10 to 1.50% by weight, an S content of usually 3500 to 7000ppm, an average particle diameter of usually 0.05 to 0.50 μm, a particlediameter of coarse particles of usually 1.00 to 5.00 μm, a saturationmagnetization value of usually 70 to 90 μm²/kg, a crystallite size of(110) plane of α-Fe of usually 200 to 300 Å, and an Fe content ofusually 65 to 70% by weight based on the weight of whole particles.

Meanwhile, although it will be generally considered that the coarse ironcomposite particles grown-up after a long-term preservation show adeteriorated penetration into soil, unexpectedly, the purifying agent ofthe present invention can exhibit an excellent purification performancewithout deterioration in penetrability into soil notwithstanding theincrease in particle diameter.

Also, the purifying agent of the present invention may contain sodiumpolyacrylate. The content of the sodium polyacrylate is usually 5 to 50%by weight, preferably 5 to 30% by weight (calculated as a solid contentthereof) based on the weight of the iron composite particles.

When the content of the sodium polyacrylate is less than 5% by weight,the sodium polyacrylate may fail to sufficiently contribute toenhancement in penetrability of the purifying agent into soil due tosuch a low content of the sodium polyacrylate. When the content of thesodium polyacrylate is more than 50% by weight, the viscosity of thepurifying agent tends to be increased, resulting in poor industrialproductivity thereof. In addition, since such a high content of thesodium polyacrylate leads to deteriorated penetrability of the purifyingagent upon injection thereof into soil, it may be difficult to attainthe aimed effects of the present invention.

The sodium polyacrylate used in the present invention usually has anumber-average molecular weight of 2000 to 10000, preferably 2500 to8000. Specific examples of the sodium polyacrylate may include“GOOD-RITE K-739” produced by NOVEON CO., LTD., “JURYMER AC-10NP”produced by NIHON JUNYAKU CO., LTD., “JURYMER AC-103” produced by NIHONJUNYAKU CO., LTD., “AQUALIC DL-100” produced by NIPPON SHOKUBAI CO.,LTD., etc.

In addition, the purifying agent of the present invention may be diluted10 to 300 times such that the concentration of the iron compositeparticles contained therein is in the range of 0.1 to 200 g/L.

Further, the purifying agent of the present invention may contain sodiumhydrogen carbonate, sodium sulfate or a mixture thereof. Theconcentration of sodium hydrogen carbonate contained in the purifyingagent is usually 0.01 to 1.0% by weight, preferably 0.01 to 0.5% byweight, and the concentration of sodium sulfate contained therein isusually 0.01 to 1.0% by weight, preferably 0.04 to 1.0% by weight.

The purifying agent containing sodium polyacrylate can be considerablyenhanced in penetrability into contaminated soil or ground water withoutsubstantial deterioration in purification performance. The reasontherefor is considered to be that the sodium polyacrylate contained inthe purifying agent acts for preventing magnetic agglomeration of theiron composite particles and reducing attraction force therebetween.

The above purifying agent is defined as follows:

(1) The purifying agent is a water suspension containing iron compositeparticles as an effective ingredient and sodium polyacrylate, in whichthe iron composite particles are composed of α-Fe and magnetite, andhave a ratio of a diffraction intensity D₁₁₀ of (110) plane of α-Fe to asum of a diffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to 0.95,preferably 0.32 to 0.95 as measured from X-ray diffraction spectrum ofthe iron composite particles, an Al content of usually 0.10 to 1.50% byweight, preferably 0.20 to 1.20% by weight, an S content of usually 3500to 7000 ppm, preferably 3800 to 6500 ppm, an average particle diameterof usually 0.05 to 0.5 μm, preferably 0.05 to 0.30 μm, a particlediameter of coarse particles of usually 0.5 to 5.0 μm, preferably 0.50to 3.0 μm, a saturation magnetization value of usually 85 to 155 μm²/kg,preferably 90 to 155 μm²/kg, a crystallite size of (110) plane of α-Feof usually 200 to 400 Å, preferably 200 to 350 Å, and an Fe content ofusually not less than 65% by weight, preferable 70 to 80% by weightbased on the weight of whole particles.

(2) The purifying agent preserved for a period of less than one month isa water suspension containing iron composite particles as an effectiveingredient and sodium polyacrylate, in which the iron compositeparticles are composed of α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.30 to 0.95,preferably 0.32 to 0.95 as measured from X-ray diffraction spectrum ofthe iron composite particles, an Al content of usually 0.10 to 1.50% byweight, preferably 0.20 to 1.20% by weight, an S content of usually 3500to 7000 ppm, preferably 3800 to 6500 ppm, an average particle diameterof usually 0.05 to 0.50 μm, preferably 0.05 to 0.30 μm, a saturationmagnetization value of usually 85 to 155 μm²/kg, preferably 90 to 155μm²/kg, a crystallite size of (110) plane of α-Fe of usually 200 to 400Å, preferably 200 to 350 Å, and an Fe content of usually not less than75% by weight, preferably 75 to 98% by weight based on the weight ofwhole particles.

(3) The purifying agent preserved for a period of not less than onemonth and less than 3 months is a water suspension containing ironcomposite particles as an effective ingredient and sodium polyacrylate,in which the iron composite particles are also composed of α-Fe andmagnetite, and have a ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311) plane ofmagnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) ofusually 0.50 to 0.80 as measured from X-ray diffraction spectrum of theiron composite particles, an Al content of usually 0.10 to 1.50% byweight, an S content of usually 3500 to 7000 ppm, an average particlediameter of usually 0.05 to 0.50 μm, a particle diameter of coarseparticles of usually 0.10 to 0.60 μm, a saturation magnetization valueof usually 100 to 140 μm²/kg, a crystallite size of (110) plane of α-Feof usually 250 to 400 Å, and an Fe content of usually 70 to 80% byweight based on the weight of whole particles.

(4) The purifying agent preserved for a period of not less than 3 monthsand less than 6 months is a water suspension containing iron compositeparticles as an effective ingredient and sodium polyacrylate, in whichthe iron composite particles are also composed of α-Fe and magnetite,and have a ratio of a diffraction intensity D₁₁₀ of (110) plane of α-Feto a sum of a diffraction intensity D₃₁₁ of (311) plane of magnetite andthe diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.30 to0.50 as measured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.50 μm, a particle diameter of coarse particles ofusually 0.30 to 1.00 μm, a saturation magnetization value of usually 90to 100 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 250to 400 Å, and an Fe content of usually 70 to 80% by weight based on theweight of whole particles.

(5) The purifying agent preserved for a period of not less than 6 monthsand less than 12 months is a water suspension containing iron compositeparticles as an effective ingredient and sodium polyacrylate, in whichthe iron composite particles are also composed of α-Fe and magnetite,and have a ratio of a diffraction intensity D₁₁₀ of (110) plane of α-Feto a sum of a diffraction intensity D₃₁₁ of (311) plane of magnetite andthe diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to0.30 as measured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.50 μm, a particle diameter of coarse particles ofusually 0.60 to 5.00 μm, a saturation magnetization value of usually 70to 90 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 250to 400 Å, and an Fe content of usually 70 to 80% by weight based on theweight of whole particles.

(6) The purifying agent preserved for a period of not less than 12months is a water suspension containing iron composite particles as aneffective ingredient and sodium polyacrylate in which the iron compositeparticles are also composed of α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to 0.30 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of usually 0.10 to 1.50% by weight, an Scontent of usually 3500 to 7000 ppm, an average particle diameter ofusually 0.05 to 0.50 μm, a particle diameter of coarse particles ofusually 1.00 to 5.00 μm, a saturation magnetization value of usually 70to 90 μm²/kg, a crystallite size of (110) plane of α-Fe of usually 200to 300 Å, and an Fe content of usually 65 to 70% by weight based on theweight of whole particles.

(7) The diluted purifying agent is a water suspension containing ironcomposite particles as an effective ingredient which are composed ofα-Fe and magnetite, and have a ratio of a diffraction intensity D₁₁₀ of(110) plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311)plane of magnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀))of usually 0.20 to 0.98, preferably 0.30 to 0.95 as measured from X-raydiffraction spectrum of the iron composite particles, an Al content ofusually 0.10 to 1.50% by weight, preferably 0.20 to 1.20% by weight, anS content of usually 3500 to 7000 ppm, preferably 3800 to 6500 ppm, andan average particle diameter of usually 0.05 to 0.50 μm, preferably 0.05to 0.30 μm, in which the concentration of the iron composite particlesin the water suspension is diluted to usually 0.1 to 200 g/L, preferably0.5 to 100 g/L.

(8) The purifying agent is a water suspension containing iron compositeparticles as an effective ingredient and sodium hydrogen carbonate,sodium sulfate or a mixture thereof, in which the iron compositeparticles are composed of α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of usually 0.20 to 0.98,preferably 0.30 to 0.98, as measured from X-ray diffraction spectrum ofthe iron composite particles, an Al content of usually 0.10 to 1.50% byweight, preferably 0.20 to 1.20% by weight, an S content of usually 3500to 7000 ppm, preferably 3800 to 6500 ppm, and an average particlediameter of usually 0.05 to 0.50 μm, preferably 0.05 to 0.30 μm, inwhich the concentration of the iron composite particles in the watersuspension is diluted to usually 0.11 to 200 g/L, preferably 0.5 to 100g/L.

Next, the process for producing the purifying iron composite particlesfor purifying soil or ground water contaminated with organohalogencompounds according to the present invention, is described.

The goethite-particles can be produced by ordinary methods, for example,by passing an oxygen-containing gas such as air through a suspensioncontaining a ferrous-containing precipitate such as hydroxides orcarbonates of iron which is obtained by reacting a ferroussalt-containing aqueous solution with at least one compound selectedfrom the group consisting of alkali hydroxides, alkali carbonates andammonia.

Meanwhile, in order to obtain the purifying iron composite particleshaving a less amount of impurities, as the ferrous salt-containingaqueous solution, there are preferably used high-purity solutions thatare reduced in content of impurities such as heavy metals.

For reducing the amount of impurities contained in the ferroussalt-containing aqueous solution, there may be used, for example, amethod in which a steel plate is washed with sulfuric acid to dissolveout, thereby removing impurities, rust-preventive oils or the like whichare deposited on the surface thereof, and then the resultantimpurity-free steel plate is dissolved to prepare a high-purity aqueousferrous salt solution. On the other hand, the use of materials obtainedby acid-washing scrap irons containing a large amount of metalimpurities other than iron, steel plates subjected to plating treatment,phosphate treatment or chromic acid treatment for improving corrosionresistance thereof, or steel plates coated with rust-preventive oils, isundesirable. This is because impurities tend to remain in the obtainediron composite particles, thereby causing such a risk that theimpurities is eluted from the iron composite particles into soil orground water to be purified. Alternatively, there may also be used amethod of adding alkali such as alkali hydroxides to a ferrous sulfatesolution by-produced from titanium oxide production process, etc., toadjust the pH value thereof; insolubilizing and precipitating titaniumas well as other impurities in the from of hydroxides thereof; and thenremoving the resultant precipitates from the reaction solution byultra-filtration, etc. Among these methods, the method of dissolving thesteel plate having a less amount of impurities with sulfuric acid ispreferred, and the method is more preferably followed by removing theimpurities from the obtained aqueous ferrous salt solution by adjustingthe pH value thereof. All of the above-described methods areindustrially applicable without problems and are also advantageous fromeconomical viewpoints.

The goethite particles used in the present invention have an averagemajor axis diameter of usually 0.05 to 0.50 μm and an S content ofusually 2200 to 4500 ppm, and may be either spindle-shaped particles oracicular particles. In addition, the goethite particles have an aspectratio of usually 4:1 to 30:1, more preferably 5:1 to 25:1, and a BETspecific surface area of usually 20 to 200 m²/g, preferably 25 to 180m²/g.

In the present invention, it is important to incorporate Al into thegoethite particles or coat the goethite particles with Al. Theincorporation or coating of Al allows a granulated product of thegoethite particles to exhibit a limited volume shrinkage, resulting inwell-controlled hardness of the granulated product. Therefore, wetpulverization of the granulated product of the goethite particles can befacilitated. Further, the size of primary particles of the goethiteparticles can be relatively reduced, resulting in relatively largespecific surface area thereof as well as enhancement in purificationperformance.

The amount of Al incorporated into or coated on the goethite particlesis usually 0.06 to 1.00% by weight.

The goethite particles are preferably previously granulated by ordinarymethods. The granulated goethite particles become usable in a fixedbed-type reducing furnace. Further, the iron composite particlesobtained from the granulated goethite particles can still maintain ashape of the granulated product under some reducing conditions and,therefore, can be suitably used for filling into columns, etc.

The hematite particles are obtained by heat-dehydrating the goethiteparticles at a temperature of 250 to 350° C.

The S content of the hematite particles can be well controlled by usinggoethite particles previously having a high S content. Also, in the caseof the goethite particles having a low S content, the S content of thehematite particles may be controlled by adding sulfuric acid to a watersuspension containing the hematite particles.

The thus obtained hematite particles have an average major axis diameterof usually 0.05 to 0.50 μm, and an S content of usually 2400 to 5000ppm. The amount of Al contained in or coated on the hematite particlesis usually 0.07 to 1.13% by weight.

The goethite particles or the hematite particles are heat-reduced at atemperature of usually 350 to 600° C. to produce iron particles (α-Fe).

When the heat-reducing temperature is less than 350° C., the reductionreaction tends to proceed too slowly, resulting in a prolonged reductionreaction time. Even though the BET specific surface area of theparticles may be increased under such a low temperature condition tofacilitate the reduction reaction, a sufficient crystal growth of theparticles tends to be inhibited, resulting in formation of unstable α-Fephase and thick oxidation film on the surface of the particles, orinsufficient phase transfer from Fe₃O₄ phase to α-Fe phase. As aresults, it may be difficult to increase the α-Fe phase content. Whenthe heat-reducing temperature is more than 600° C., the reductionreaction tends to proceed too rapidly, so that sintering within orbetween the particles is excessively accelerated, resulting in a toolarge particle size and a too small BET specific surface area of theobtained particles.

Meanwhile, as the heating atmosphere upon the reduction reaction, theremay be used hydrogen gas, nitrogen gas or the like. Among theseatmospheres, hydrogen gas is preferred from industrial viewpoints.

The iron particles obtained after the heat-reduction are cooled, andthen taken out and transferred into water without forming an oxidationfilm (layer) on the surface of the iron particles in a gas phase.Thereafter, the oxidation film (layer) is formed on the surface of theiron particles in water, and the thus obtained iron particles having theoxidation film (layer) thereon are then dried.

As the cooling atmosphere, there may be used either nitrogen orhydrogen. However, at a final stage of the cooling, the atmosphere ispreferably changed to nitrogen atmosphere. When the iron particles aretransferred into water, the iron particles are preferably cooled to atemperature of not more than 100° C.

The drying atmosphere may be appropriately selected from nitrogen, air,vacuum, etc. The drying temperature is usually not more than 100° C.

In the above heat-reduction treatment, the particles are transformedinto iron particles composed of α-Fe phase as a whole. When transferringthe iron particles into water, water is decomposed into oxygen andhydrogen by catalytic activity of the α-Fe. As a result, it isconsidered that the α-Fe is oxidized by the oxygen generated, so that anoxidation film (layer) composed of Fe₃O₄ is formed on the surface of theparticles.

Next, the process for producing the purifying agent for purifying soilor ground water contaminated with organohalogen compounds according tothe present invention, is described. In the process of the presentinvention, the iron particles obtained after the heat-reduction arecooled, and then taken out and transferred into water. The resultantwater suspension containing the iron composite particles can be directlyused as a purifying agent.

The purifying agent of the present invention is preferably in the formof a dispersion obtained by dispersing pulverized secondary agglomeratesof the iron composite particles in water.

Thus, the iron composite particles are preferably pulverized by wetpulverization method in the consideration of agglomeration condition,properties (high-activity), particle size, capacity of pulverizer(particle size of product and amount pulverized) and final configurationof the iron composite particles.

The iron particles obtained after the heat-reduction treatment arecooled, and then taken out and transferred in water, in which the ironparticles are oxidized to form an oxidation film on the surface thereof.Thereafter, the thus obtained iron composite particles are suitablywet-pulverized.

As the pulverizer usable in the present invention, in the case wheregrinding media are employed, there may be used media-stirring type millsincluding vessel-drive type mills, e.g., rolling mills such as pot mill,tube mill, conical mill, vibration mills such as fine vibration mill, orthe like; and media-agitation type mills, e.g., tower type mills such astower mill, agitation tank type mills such as attritor, flowing tubetype mills such as sand grind mill, annular type mills such as annularmill, or the like. In the case where no grinding media are employed,there may be used shear/friction type mills, e.g., vessel rotating typemills such as Wong mill, wet high-speed rotation type mills such ascolloid mill, homomixer and line mixer, or the like.

In general, the pulverization means a procedure of crushing rawmaterials having a size of not more than 25 mm into particles, andgenerally classified into coarse pulverization, minute pulverization andfine pulverization. The coarse pulverization is to pulverize the rawmaterials into particles having a size of 5 mm to 20 mesh, the minutepulverization is to pulverize the raw materials into particlescontaining small particles having a size of not more than 200 mesh in anamount of about 90%, and the fine pulverization is to pulverize the rawmaterials into particles containing fine particles having a size of notmore than 325 mesh in an amount of about 90%. Further, there is known anultrafine pulverization in which the raw materials are pulverized intoseveral microns. In the present invention, the iron composite particlesare preferably successively subjected to three pulverization treatmentsincluding the coarse pulverization, minute pulverization and finepulverization.

The coarse pulverization may be carried out using a stirrer of alow-speed rotation type, a medium-speed rotation type, a high-speedrotation shearing type or a high- and low-speed combined rotation typewhich is inserted into an agitation tank equipped with a baffle. Inparticular, in the consideration of pulverization of agglomerates of theiron composite particles, the medium- to high-speed rotation typestirrer that can be operated at 1000 to 6000 rpm is preferably used. Asthe blade of these stirrers, there may be used disk turbine, fanturbine, arrow feather-shaped turbine, propeller-type turbine, etc. Ofthese stirrers, preferred are edged disk turbines, for example,homodisper manufactured by Tokushu Kika Kogyo Co., Ltd.

The minute or fine pulverization may be carried out using a batch typeapparatus or a continuous type apparatus. Of these apparatuses, thecontinuous type apparatus is preferred from industrial viewpoints. Theminute or fine pulverization using grinding media may be carried outusing ball mill, tower mill, sand grind mill, attritor or the like.Also, the minute or fine pulverization using no grinding media may becarried out using homomixer, line mixer or the like.

In the minute pulverization, there may be used such a pulverizer havinga multi-stage structure which includes the combination of a stator and arotor provided at its outer periphery with a plurality of slits as ashaft-fixing surface portion into which cutter blades are fitted. Inparticular, a continuous shear dispersing apparatus such as media-lessline mixer whose rotor is rotated at a peripheral speed of not less than30 m/s, for example, “Homomic Line Mixer” manufactured by Tokushu KikaKogyo Co., Ltd., is preferred.

The fine pulverization (finish pulverization) may be carried out using amedia type dispersing apparatus such as a sand grind mill in which aplurality of disks fitted on a rotating axis disposed at a center of acylindrical vessel filled with φ1 to φ3 grinding media at a fillingpercentage of 70 to 80%, are rotated to cause a rapid rotation action ofthe media through which materials to be treated are passed fromunderneath to above. For example, a sand grinder manufactured by ImexInc., is more preferred.

In the wet pulverization of the present invention, in order toaccelerate formation of cracks in the particles and inhibition ofrebinding the pulverized particles, or in order to prevent the particlesfrom being agglomerated into granular particles which are difficult topulverize, or prevent the particles from being adhered onto balls ormills which may cause deterioration in pulverizing force thereof,suitable pulverizing assistants may be appropriately added to theparticles to be pulverized. The pulverizing assistants may be in theform of either solid or liquid. Examples of the solid pulverizingassistants may include stearic acid salts, colloidal silica, colloidalcarbon or the like. Examples of the liquid pulverizing assistants mayinclude triethanolamine, alkyl sulfonates or the like.

The concentration of the iron composite particles contained in the watersuspension upon the wet pulverization is usually 20 to 40% by weight.When the concentration of the iron composite particles is less than 20%by weight, it may be difficult to apply a suitable stress such as shearforce upon the pulverization, thereby failing to pulverize the ironcomposite particles into the aimed particle size, or resulting inprolonged pulverization time. Further, the grinding media required forthe wet pulverization may suffer from severe abrasion. When theconcentration of the iron composite particles is more than 40% byweight, the water suspension may exhibit a too high viscosity, therebyrequiring a large mechanical load, so that it may be difficult toindustrially produce the aimed particles.

The purifying agent containing sodium polyacrylate may be produced bydissolving sodium polyacrylate in water to prepare an aqueous sodiumpolyacrylate solution, and then adding the thus prepared solution intothe water suspension containing the iron composite particles.

Also, the purifying agent containing sodium hydrogen carbonate and/orsodium sulfate is preferably produced by diluting the purifying agentobtained by the above production method with an appropriate diluent, andthen adding a predetermined amount of sodium hydrogen carbonate and/orsodium sulfate into the diluted purifying agent. In this case, as thediluent, there may be used ion-exchanged water.

Next, the method for purifying soil or ground water contaminated withorganohalogen compounds according to the present invention, isdescribed.

The purification treatment of soil or ground water contaminated withorganohalogen compounds is generally classified into the “in-situdecomposition” method in which contaminants contained therein aredirectly decomposed under the ground, and the “in-situ extraction”method in which soil or ground water containing contaminants isexcavated or extracted and then the contaminants contained therein aredecomposed in place. In the present invention, both of these methods areusable.

In the in-situ decomposition method, the purifying iron compositeparticles or the purifying agent may be directly penetrated into theunderground, or introduced into the underground through drilled bore,using a transferring medium including gas media such as high-pressureair and nitrogen or water. In particular, since the purifying agent ofthe present invention is in the form of a water suspension, thepurifying agent may be directly used, or may be used in the form of adiluted solution.

In the in-situ extraction method, the excavated soil may be mixed andstirred with the purifying iron composite particles or the purifyingagent using sand mill, Henschel mixer, concrete mixer, Nauter mixer,single- or twin-screw kneader type mixer, or the like. Also, the pumpedground water may be passed through a column, etc., which are filled withthe purifying iron composite particles.

The concentration of the purifying iron composite particles or thepurifying agent added may be appropriately determined according to thedegree of contamination of soil or ground water with organohalogencompounds. In the case where contaminated soil is to be purified, theconcentration of the purifying iron composite particles or the purifyingagent added is usually 0.1 to 200 g/L, preferably 0.5 to 100 g/L basedon 1000 g of the soil. When the concentration of the purifying ironcomposite particles or the purifying agent added is less than 0.1 g/L,it may be difficult to attain the aimed effects of the presentinvention. When the concentration of the purifying iron compositeparticles or the purifying agent added is more than 200 g/L, althoughthe purification effect is enhanced, the use of such a large amount ofthe purifying iron composite particles or the purifying agent isuneconomical. Also, in the case where contaminated ground water is to bepurified, the concentration of the purifying iron composite particles orthe purifying agent added is usually 0.1 to 200 g/L, preferably 0.5 to100 g/L based on 1000 g of the ground water.

When the organohalogen compounds contained in the soil or ground waterare purified using the purifying iron composite particles or thepurifying agent of the present invention, the apparent reaction rateconstant can be increased to not less than 0.005 h⁻¹ as measured by thebelow-mentioned evaluation method.

Next, the method for purifying soil or ground water contaminated withharmful heavy metals or the like according to the present invention, isdescribed.

The soil or ground water contaminated with harmful heavy metals or thelike may be purified by the “containment” method. In the presentinvention, both of “in-situ containment” and “containment afterexcavation” methods are applicable.

In the “in-situ containment” method, a mixture of the purifying ironcomposite particles and water or the purifying agent may be directlypenetrated into the underground, or introduced into the undergroundthrough drilled bore, using gas media such as high-pressure air andnitrogen. Since the purifying agent is in the form of a watersuspension, the purifying agent may be directly used, or may be used inthe form of a diluted solution, if required.

In the “containment after excavation” method, a mixture of the purifyingiron composite particles and water or the purifying agent may be mixedand stirred with contaminated soil using sand mill, Henschel mixer,concrete mixer, Nauter mixer, single- or twin-screw kneader type mixer,or the like, thereby incorporating the heavy metals or the likecontained in the soil into ferrite as produced, and then confining theheavy metals or the like therein. Meanwhile, if required, the ferrite inwhich the heavy metals are incorporated and confined may be magneticallyseparated from the soil.

The concentration of the purifying iron composite particles or thepurifying agent added may be appropriately determined according to thedegree of contamination of soil or ground water with harmful heavymetals or the like. In the case where contaminated soil is to bepurified, the concentration of the purifying iron composite particles orthe purifying agent added is usually 0.1 to 200 g/L, preferably 0.5 to100 g/L based on 1000 g of the soil. When the concentration of thepurifying iron composite particles or the purifying agent added is lessthan 0.1 g/L, it may be difficult to attain the aimed effects of thepresent invention. When the concentration of the purifying ironcomposite particles or the purifying agent added is more than 200 g/L,although the purification effect is enhanced, the use of such a largeamount of the purifying iron composite particles or the purifying agentis uneconomical. Also, in the case where contaminated ground water is tobe purified, the concentration of the purifying iron composite particlesor the purifying agent added is usually 0.1 to 200 g/L, preferably 0.5to 100 g/L based on 1000 g of the ground water.

In addition, in the case where the purifying agent used contains any ofsodium polyacrylate, sodium hydrogen carbonate and sodium sulfate, thesolid content of the iron composite particles in the purifying agent ispreferably 0.1 to 200 g/L, more preferably 0.5 to 100 g/L.

When the harmful heavy metals or the like contained in the soil orground water are purified or insolubilized using the purifying ironcomposite particles or the purifying agent of the present invention, theapparent reaction rate constant can be increased to not less than 0.01h⁻¹ for arsenic, not less than 0.01 h⁻¹ for chromium and not less than0.05 h⁻¹ for lead as measured by the below-mentioned evaluation method.

In the case where the purifying agent of the present invention ispenetrated into soil, the penetration percentage thereof can beincreased to not less than 100%, more preferably not less than 200% asmeasured by the below-mentioned evaluation method.

The point of the present invention is that by using the purifying ironcomposite particles or the purifying agent of the present invention,organohalogen compounds contained in soil or ground water can beeffectively and economically decomposed.

The reasons why the organohalogen compounds contained in soil or groundwater can be effectively decomposed, are considered as follows, thoughit is not clearly determined.

That is, it is considered that in the purifying iron composite particlesof the present invention, since the α-Fe phase (0 valence) and Fe₃O₄phase are present therein at a specific ratio, and a part of sulfur ispresent in a 0 valence form through the heat reduction step, the ironcomposite particles can exhibit a high reducing activity and, therefore,contribute to the decomposition reaction of the organohalogen compounds.

In the present invention, by adding a specific amount of the Al compoundto the purifying iron composite particles, the iron composite particlescan be enhanced in decomposition activity to the organohalogencompounds. The reason therefor is considered as follows, though it isnot clearly determined. That is, by incorporating Al into the ironcomposite particles, the primary particles thereof become finer, andagglomerates of the iron composite particles show a lower strength ascompared to the conventional particles. Therefore, it becomes possibleto wet-pulverize the iron composite particles into fine particles with aless difficulty as compared to the case where the same pulverizationmethod is applied to the conventional particles. As a result, it isconsidered that since the iron composite particles are readilypenetrated and dispersed into the soil or ground water, thedecomposition activity to organohalogen compounds which is inherent tothe iron composite particles can be sufficiently exhibited.

As described above, since the purifying iron composite particles of thepresent invention exhibit a high catalytic activity, the purificationtreatment can be efficiently performed for a short period of time. Inparticular, the purifying iron composite particles of the presentinvention are suitable for purifying the soil or ground watercontaminated with a high-concentration organohalogen compounds.

Also, since the purifying iron composite particles of the presentinvention have a fine particle size and a high activity, α-Fe containedtherein is readily dissolved at ordinary temperature without heating.Further, since the iron composite particles allows water contained inthe soil or ground water to be efficiently decomposed into hydrogen orhydroxyl groups, a local alkaline region is always present in the soilor ground water, so that the dissolution reaction of α-Fe can proceedgradually. Then, the dissolved α-Fe is continuously reacted with theharmful heavy metals or the like on the interfacial region of the ironcomposite particles while incorporating hydroxyl groups and oxygenproduced by the decomposition of water or dissolved oxygen thereinto. Asa result, it is considered by the present inventors that formation ofspinel ferrite is continuously caused so that the harmful heavy metalsor the like are incorporated and insolubilized therein. Further, it isalso considered that S contained in the iron composite particles alsocontributes to local dissolution of α-Fe.

In addition, it is considered by the present inventors that the ferriteformation reaction between the dissolved α-Fe and the harmful heavymetals or the like causes an epitaxial growth of particles around spinelmagnetite present in the surface layer as a seed, resulting in efficientinsolubilization of the harmful heavy metals or the like.

In the present invention, since any forcible oxidation treatments suchas pH adjusting treatment by addition of acid or alkali, heat treatmentand air-blowing treatment are not required, the harmful heavy metals orthe like can be efficiently insolubilized.

Further, in the present invention, the insolubilized heavy metals or thelike can be prevented from being eluted out again as described inExamples below. Therefore, the insolubilized heavy metals or the likecan be kept in a harmless state for a long period of time.

As described above, the purifying iron composite particles of thepresent invention enable the organohalogen compounds and/or heavy metalsor the like to be efficiently decomposed and insolubilized, and are,therefore, suitable as a purifying agent for soil or ground water.

Also, the purifying agent of the present invention containing sodiumpolyacrylate can be improved in penetrability into soil, and thepurifying agent containing sodium hydrogen carbonate and/or sodiumsulfate can also be improved in penetrability into soil.

Further, in the case where the purifying agent of the present inventioncontains sodium polyacrylate, the penetrability of the purifying agentinto soil can be remarkably enhanced. As a result, the number ofinjection sites of the purifying agent can be reduced, and the workingefficiency can be enhanced, resulting in shortened working period andeconomically advantageous purification treatment.

In addition, in the case where the purifying agent of the presentinvention contains sodium hydrogen carbonate and/or sodium sulfate, thepenetrability of the purifying agent into soil can also be remarkablyenhanced. As a result, the number of injection sites of the purifyingagent can be reduced, and the working efficiency can be enhanced,resulting in shortened working period and economically advantageouspurification treatment.

EXAMPLES

The present invention is described in more detail by Examples andComparative Examples, but the Examples are only illustrative and,therefore, not intended to limit the scope of the present invention.

Various properties were evaluated by the following methods.

(1) The average major axis diameter and the aspect ratio of goethiteparticles were measured from a transmission electron micrograph thereof(magnification: ×30000). The average particle diameters of hematiteparticles and iron composite particles were measured from a scanningelectron micrograph thereof (magnification: ×30000).

(2) The Fe and Al contents in the iron composite particles as well asthe As, Cr and Pb contents in a filtrate obtained by the solid-liquidseparation after the insolubilization of heavy metals or the like, weremeasured using an inductively coupled high-frequency plasma atomicemission spectroscope “SPS-4000” manufactured by Seiko Denshi Kogyo Co.,Ltd.

(3) The S content of the respective particles was measured using “Carbonand Sulfur Analyzer EMIA-2200” manufactured by Horiba Seisakusho Co.,Ltd.

(4) The crystal phase of the respective particles was identified bymeasuring a crystal structure of the particles in the range of 10 to 90°by X-ray diffraction method.

(5) The peak intensity ratio of the iron composite particles wasdetermined by measuring a diffraction intensity D₁₁₀ of (110) plane ofα-Fe and a diffraction intensity D₃₁₁ of (311) plane of magnetite fromthe results of the above X-ray diffraction measurement and calculating aratio of D₁₁₀/(D₃₁₁+D₁₁₀)

(6) The crystallite size ((110) plane of α-Fe) of the iron compositeparticles was expressed by the thickness of crystallite in the directionperpendicular to each crystal plane of the particles as measured byX-ray diffraction method. The thickness value was calculated from theX-ray diffraction peak curve prepared with respect to each crystal planeaccording to the following Scherrer's formula:

Crystallite Size D₁₁₀ =Kλ/β cos θ

wherein β is a true half value-width of the diffraction peak which wascorrected as to the width of machine used (unit: radian); K is aScherrer constant (=0.9); λ is a wavelength of X-ray used (Cu Kα-ray0.1542 nm); and θ is a diffraction angle (corresponding to diffractionpeak of each crystal plane).

(7) The specific surface area of the respective particles was expressedby the value measured by BET method using “Monosorb MS-11” manufacturedby Cantachrom Co., Ltd.

(8) The saturation magnetization value of the iron composite particleswas measured using a vibration sample magnetometer “VSM-3S-15”manufactured by Toei Kogyo Co., Ltd., by applying an external magneticfield of 795.8 kA/m (10 kOe) thereto.

(9) The particle size distribution of the iron composite particlescontained in the purifying agent was measured by a laser scatteringdiffraction type device “NIKKISO MICROTRAC HRA MODEL 9320-X100”manufactured by Nikkiso Co., Ltd. Meanwhile, upon the measurement,ethanol and organosilane were used as dispersing solvent and dispersant,respectively, and the particles were dispersed therein using anultrasonic dispersing apparatus for one minute.

(10) The amounts of elution of elements other than iron contained in theiron composite particles including cadmium, lead, chromium, arsenic,whole mercury, selenium, whole cyanogen, fluorine and boron, weremeasured according to “Environmental Standard for Contamination ofSoil”, Notification No. 46 of the Environmental Agency of Japan,

(11) The measurements of the organohalogen compounds were conducted bythe following methods:

<Preparation of Calibration Curve: Quantitative Determination ofOrganohalogen Compounds>

The concentration of the organohalogen compounds was calculated from thecalibration curve previously prepared according to the followingprocedure.

Trichloroethylene (TCE: C₂HCl₃): molecular weight: 131.39; guaranteedreagent (99.5%); density (at 20° C.): 1.461 to 1.469 g/mL

Trichloroethylene was used in three standard amounts (0.05 μL, 0.1 μLand 1.0 μL) in this procedure. 30 mL of ion-exchanged water was added toa 50-mL brown vial bottle (effective capacity: 68 mL). Next, after therespective standard amounts of trichloroethylene were poured into eachvial bottle, the vial bottle was immediately closed with a rubber plugwith a fluororesin liner, and then an aluminum seal was firmly tightenedon the rubber plug. After allowing the vial bottle to stand at 20° C.for 20 min, 50 μL of a headspace gas in the vial bottle was sampledusing a syringe, and the amount of trichloroethylene contained in thesampled gas was measured by “GC-MS-QP5050” manufactured by ShimadzuSeisakusho Co., Ltd. Assuming that trichloroethylene was not decomposedat all, the relationship between the amount of trichloroethylene addedand the peak area was determined from the measured values. The aboveanalysis was carried out using a capillary column (“DB-1” manufacturedby J & B Scientific Co. Ltd.; liquid phase: dimethyl polysiloxane) andHe gas (flow rate: 143 L/min) as a carrier gas. Specifically, the samplewas held at 40° C. for 2 min and then heated to 250° C. at a temperaturerise rate of 10° C./min for analyzing the gas.

<Preparation of Samples for Measurement of Organohalogen Compounds (A)>

A 50-mL brown vial bottle (effective capacity: 68 mL) was filled with0.1 g of the purifying iron composite particles and 30 mL ofion-exchanged water. Next, after 1 μL of trichloroethylene was pouredinto the vial bottle, the vial bottle was immediately closed with arubber plug with a fluororesin liner, and an aluminum seal was firmlytightened on the rubber plug.

<Evaluation Method for Decomposition Reaction of Organohalogen Compounds(Measurement of Apparent Reaction Rate Constant>

The above vial bottle was allowed to stand at 24° C. After furtherallowing the vial bottle to stand at 20° C. for 20 min, 50 μL of aheadspace gas in the vial bottle was sampled using a syringe. Meanwhile,the headspace gas was sampled up to maximum 500 hours at predeterminedtime intervals by batch method, and was analyzed by “GC-MS-QP5050”manufactured by Shimadzu Seisakusho Co., Ltd., to measure theconcentration of residual trichloroethylene contained in the gas.

The reaction rate constant kobs was calculated from the measuredconcentration of residual trichloroethylene according to the followingformula:

ln(C/C ₀)=−k·t

wherein C₀ is an initial concentration of trichloroethylene; C is aresidual concentration of trichloroethylene; k is an apparent reactionrate constant (h⁻¹); and t is a time (h).

(12) The measurements of the heavy metals or the like were conducted bythe following methods.

<Preparation of Samples for Measurement of Heavy Metals or the Like andEvaluation Method for Insolubilization Reaction (Measurement of ApparentReaction Rate Constant)>

25 mL of a 1000 ppm standard solution (produced by Kanto Kagaku Co.,Ltd.) was sampled in a 1000 mL measuring flask such that concentrationsof arsenic, chromium and lead in the solution were 25 ppm, and thenion-exchanged water was added to the flask to prepare total 1000 mL of aheavy metal-containing solution. A 50-mL brown vial bottle (effectivecapacity: 68 mL) was filled with 0.06 g of the purifying iron compositeparticles and 30 mL of the above-prepared heavy metal-containingsolution, and then immediately closed with a rubber plug and allowed tostand at 24° C. The contents in the vial bottle were subjected tosuction filtration using a 0.45 μm membrane filter in order to separatethe solution from the iron composite particles, thereby preparing asample solution for measuring amounts of residual heavy metals.Meanwhile, the solution was sampled at predetermined time intervals upto maximum 336 hours, and the residual concentrations of the heavymetals in the solution were measured by batch method.

<Evaluation Method for Heavy Metals>

The obtained solution was analyzed using an inductively coupledhigh-frequency plasma atomic emission spectroscope “SPS-4000”manufactured by Seiko Denshi Kogyo Co., Ltd., to measure theresidual-concentration of the respective heavy metals in the solution.

Meanwhile, the measurement was performed by a calibration curve method.Specifically, a calibration curve was prepared with respect to 4 or moreconcentration standards, and the measurement was conducted by thecalibration curve in which a correlation coefficient thereof was 0.9999or higher.

Assuming that the relation between insolubilizing time and logarithm of(residual heavy metal concentration)/(initial heavy metal concentration)is approximated to a linear expression, the apparent reaction rateconstant kobs was calculated from the measured values according to thefollowing formula:

ln(C/C ₀)=−k·t

wherein C₀ is an initial concentration of heavy metals; C is a residualconcentration of heavy metals; k is an apparent reaction rate constant(h⁻¹); and t is a time (h).<Heavy Metal Elution Test Using Acid or Alkali after Insolubilization>

According to “Report of Sectional Meeting for Studies on Stability ofSoil Treated for Insolubilization of Heavy Metals, etc.; Acid-AddedElution Testing Method; Alkali-Added Elution Testing Method” proposed bySoil Environment Center, the acid-added and alkali-added elution testswere conducted.

(Abstract of the Above Proposal)

In the case where the insolubilization-treated soil is evaluated for itsstability upon exposure to acidic or alkaline water, it is recommendedto conduct, in addition to the elution test prescribed by NotificationNo. 46 of the Environmental Agency of Japan, the sulfuric acid-addedelution test I and the calcium hydroxide-added elution test I.

If no elution of heavy metals or the like is detected through theseelution tests, the insolubilization technique is considered to be apractical and stable insolubilization treatment, and it is alsoconsidered that in the case where the insolubilized soil is returned tooriginal place, any elution of heavy metals or the like is subsequentlyno longer caused even when exposed to acid or alkali to some extent.

<Preparation of Samples Used in Elution Test for Insolubilized HeavyMetals> (1) Arsenic

A 50-mL brown vial bottle (effective capacity: 68 mL) was filled withthe above purifying agent containing 8 g/L of the iron compositeparticles, and a 20 mg/L arsenic solution (produced by Kanto Kagaku Co.,Ltd.). Then, after ion-exchanged water was added to the vial bottle toadjust a total volume of the solution in the vial bottle to 30 mL, thevial bottle was immediately closed with a rubber plug with a fluororesinliner, and then an aluminum seal was firmly tightened on the rubberplug. After allowing the vial bottle to stand at 24° C., the contentsthereof were subjected to solid-liquid separation using a 0.45 μmmembrane filter by a batch method. The resultant filtrate was analyzedusing an inductively coupled high-frequency plasma atomic emissionspectroscope “SPS-4000” manufactured by Seiko Denshi Kogyo Co., Ltd.,and a pH value thereof was measured. The solid obtained after thesolid-liquid separation was subjected to the acid/alkali-added elutiontests proposed by Soil Environment Center after the elapse of 21 dayssolely.

(2) Chromium (VI)

The same procedure for arsenic as described above was conducted exceptthat the purifying agent containing 12 g/L of the iron compositeparticles was used, and a 50 mg/L chromium (VI) solution (produced byKanto Kagaku Co., Ltd.) was added.

(3) Lead

The same procedure as described above was conducted except that thepurifying agent containing 1 g/L of the iron composite particles wasused, and a 20 mg/L lead solution (produced by Kanto Kagaku Co., Ltd.)was added.

<Preparation of Samples for Measurements of Aliphatic OrganohalogenCompounds (B)>

A 50-mL brown vial bottle (effective capacity: 68 mL) was filled with 1g of the purifying iron composite particles and 30 mL of ion-exchangedwater. Next, after 1 μL of trichloroethylene was poured into the vialbottle, the vial bottle was immediately closed with a rubber plug with afluororesin liner, and then an aluminum seal was firmly tightened on therubber plug. The contents in the vial bottle were shaken for 3 hoursusing a paint conditioner (manufactured by Red Devil Co., Ltd.).

<Evaluation Method for Aliphatic Organohalogen Compounds>

Then, 50 μL of a headspace gas in the vial bottle was sampled using asyringe, and the residual amount of trichloroethylene contained in thesampled gas was measured by “GC-MS-QP5050” manufactured by ShimadzuSeisakusho Co., Ltd.

Penetrability Test:

About a half volume of a glass column having a diameter of 3 cm and alength of 50 cm was previously filled with ion-exchanged water. Then,quartz sand having a particle size distribution thereof shown in FIG. 7,was little by little dropped into the glass column and fully filledtherein while shaking the column, thereby forming a saturated soillayer. Meanwhile, the saturated soil layer had initial characteristicvalues including a porosity of 41.3% and a coefficient of waterpermeability of 2.43×10⁻² cm/S.

The dilute purifying agent was prepared by adding ion-exchanged waterinto a mixture of 12.8 mL of the purifying agent containing 4 g of theiron composite particles and an aqueous solution containing 0.67 g ofsodium polyacrylate such that a total amount of water contained in theaqueous sodium polyacrylate solution and the purifying agent, and theion-exchanged water added was 500 mL.

Next, 500 mL of the above diluted purifying agent was poured into anupper portion of the saturated soil layer filled in the glass columnwhile maintaining a dropping height of 2 cm above the surface of thesaturated soil layer so as to keep the filling pressure constant,thereby conducting a penetrability test by gravity filling method. Theglass column was visually observed to examine the degree of penetrationof the purifying agent into the soil after completion of pouring a wholeamount of the purifying agent.

<Preparation of Samples for Decomposition Test of OrganohalogenCompounds (Object to be Tested: Water) (C)>

A 50-mL brown vial bottle (effective capacity: 68 mL) was filled withthe purifying agent as well as ion-exchanged water such that the amountof the iron composite particles contained in the purifying agent was0.06 g and a total amount of water contained in the purifying agent andion-exchanged water was 30 mL. Next, after 1.0 μL of trichloroethylenewas poured into the vial bottle, the vial bottle was immediately closedwith a rubber plug with a fluororesin liner, and then an aluminum sealwas firmly tightened on the rubber plug.

In addition, a separate 50 mL brown vial bottle (effective capacity: 68mL) was filled with the purifying agent as well as a solution containing0.01 g of sodium polyacrylate such that the amount of the iron compositeparticles contained in the purifying agent was 0.06 g and a total amountof water contained in the purifying agent and water contained in thesodium polyacrylate solution was 30 mL. Next, after 1.0 μL oftrichloroethylene was poured into the vial bottle, the vial bottle wasimmediately closed with a rubber plug with a fluororesin liner, and thenan aluminum seal was firmly tightened on the rubber plug.

The respective vial bottles were tested by the same method as describedin the above “Evaluation method for decomposition reaction oforganohalogen compounds (measurement of apparent reaction rate constant”to measure the concentration of residual trichloroethylene and calculatethe reaction rate constant Kobs from the measured value.

<Preparation of Samples for Decomposition Test of OrganohalogenCompounds (Object to be Tested: Soil) (D)>

1.0 μL of trichloroethylene was previously added to 20 g of wet sandysoil (under 2 mm mesh sieve) to prepare a soil contaminated withtrichloroethylene. A 50-mL brown vial bottle (effective capacity: 68 mL)was filled with the purifying agent as well as ion-exchanged water suchthat the amount of the iron composite particles contained in thepurifying agent was 0.06 g and a total amount of water contained in thepurifying agent and ion-exchanged water was 30 mL. Next, after theabove-prepared contaminated soil was filled into the vial bottle, thevial bottle was immediately closed with a rubber plug with a fluororesinliner, and then an aluminum seal was firmly tightened on the rubberplug.

In addition, 1.0 μL of trichloroethylene was previously added to 20 g ofwet sandy soil (under 2 mm mesh sieve) to prepare a soil contaminatedwith trichloroethylene. A separate 50-mL brown vial bottle (effectivecapacity: 68 mL) was filled with the purifying agent as well as asolution containing 0.01 g of sodium polyacrylate such that the amountof the iron composite particles contained in the purifying agent was0.06 g and a total amount of water contained in the purifying agent andwater contained in the sodium polyacrylate solution was 30 mL. Next,after the above-prepared contaminated soil was filled into the vialbottle, the vial bottle was immediately closed with a rubber plug with afluororesin liner, and then an aluminum seal was firmly tightened on therubber plug.

The respective vial bottles were tested by the same method as describedin the above “Evaluation method for decomposition reaction oforganohalogen compounds (measurement of apparent reaction rate constant”to measure the concentration of residual trichloroethylene and calculatethe reaction rate constant Kobs from the measured value.

Example 1 Production of Purifying Iron Composite Particles and PurifyingAgent

A reaction vessel maintained under a non-oxidative atmosphere by flowingN₂ gas at a rate of 3.4 cm/s, was charged with 704 L of a 1.16 mol/LNa₂CO₃ aqueous solution, and then with 296 L of an aqueous ferroussulfate solution containing 1.35 mol/L of Fe²⁺ (amount of Na₂CO₃: 2.0equivalents per equivalent of Fe), and the contents in the reactionvessel were reacted with each other at 47° C. to produce FeCO₃.

The aqueous solution containing the thus obtained FeCO₃ was successivelyheld at 47° C. for 70 min while blowing N₂ gas thereinto at a rate of3.4 cm/s. Thereafter, air was passed through the FeCO₃-containingaqueous solution at 47° C. and a flow rate of 2.8 cm/s for 5.0 hours,thereby producing goethite particles. Meanwhile, it was confirmed thatthe pH value of the aqueous solution during the air passage wasmaintained at 8.5 to 9.5.

The water suspension containing the thus obtained goethite particles wasmixed with 20 L of an aqueous Al sulfate solution containing 0.3 mol/Lof Al³⁺, and the resultant mixture was sufficiently stirred and thenwashed with water using a filter press, thereby obtaining a press cake.The obtained press cake was extrusion-molded and granulated using acompression-molding machine equipped with a mold plate having an orificediameter of 4 mm, and then dried at 120° C., thereby obtaining agranulated product of the goethite particles.

It was confirmed that the goethite particles constituting the obtainedgranulated product were spindle-shaped particles having an average majoraxis diameter of 0.30 μm, an aspect ratio (major axis diameter/minoraxis diameter) of 12.5:1, a BET specific surface area of 85 m²/g, an Alcontent of 0.40% by weight and an S content of 400 ppm.

The granulated product of the goethite particles were heated at 330° C.to form hematite particles, and then dry-pulverized. Thereafter, theobtained hematite particles were deaggregated in water, and mixed with70% sulfuric acid in an amount of 10 mL/kg under stirring. Then, theresultant mixture was dehydrated to obtain a press cake. The obtainedpress cake was extrusion-molded and granulated using acompression-molding machine equipped with a mold plate having an orificediameter of 3 mm, and then dried at 120° C., thereby obtaining agranulated product of the hematite particles.

It was confirmed that the hematite particles constituting the obtainedgranulated product were spindle-shaped particles having an average majoraxis diameter of 0.24 μm, an aspect ratio (major axis diameter/minoraxis diameter) of 10.7:1, and an S content of 3300 ppm.

100 g of the granulated product of the goethite particles wereintroduced into a fixed bed type reducing apparatus, and reduced at 450°C. for 180 min while passing H₂ gas therethrough until the goethiteparticles were completely transformed into α-Fe. Then, after replacingthe H₂ gas with N₂ gas and cooling the obtained iron particles to roomtemperature, 300 ml of ion-exchanged water was directly introduced intothe reducing furnace, and the contents of the reducing furnace weredirectly taken out therefrom in the form of a water suspensioncontaining the iron particles in an amount of about 20% by weight.

The water suspension was transferred into a stainless steel beakerequipped with a baffle, and stirred at a rotating speed of 3600 rpm for3-0 min using a medium-speed rotation type stirrer “0.2 kW-powered T.K.Homodisper 2.5 Model” with 40 mmφ edged turbine blades (manufactured byTokushu Kika Kogyo Co., Ltd.) which was inserted into the beaker.

Then, the water suspension was dispersed at a rotating speed of 4000 rpmusing a continuous shear type dispersing apparatus “0.55 kW-powered T.K.Homomic Line Mill PL-SL Model” manufactured by Tokushu Kika Kogyo Co.,Ltd.

Thereafter, the water suspension was dispersed at a rotating speed of500 rpm using a media type dispersing apparatus “1.5 kW-poweredfour-cylinder sand grinder 4-TSG-(1/8G) Model” manufactured by TokushuKika Kogyo Co., Ltd. which was filled with 0.25 L of 2 mmφ glass beads,thereby obtaining a purifying agent.

It was confirmed that the thus obtained purifying agent had a specificgravity of 1.25, a solid content of 30% by weight, a particle sizedistribution (of water suspension) with a single peak as measured bylaser diffraction scattering method, a median diameter (D₅₀) of 1.90 μm,a ratio (D₉₈/D₁₀) of 1.81 and a distribution width (D₈₄-D₁₆) of 1.10 μm.

As a result of observing by a scanning electron microscope (×30,000), itwas confirmed that the primary particles of the iron composite particlescontained in the thus obtained purifying agent are rice grain-likeparticles having an average major axis diameter of 0.09 μm and an aspectratio of 1.4:1.

Next, the water suspension was filtered to separate the iron compositeparticles therefrom, and the iron composite particles were dried in airat 40° C. for 3 hours, thereby producing purifying iron compositeparticles.

As a result, it was confirmed that the thus obtained iron compositeparticles contained α-Fe as a main component, and had a saturationmagnetization value of 135 Am²/kg (135 emu/g), a BET specific surfacearea of 27 m²/g, a crystallite size of 295 Å, an Fe content of 83.0% byweight and an S content of 4000 ppm. Also, as a result of the X-raydiffraction analysis of the iron composite particles, it was confirmedthat both of α-Fe and Fe₃d₄ were present therein, and the ratio of adiffraction intensity D₁₁₀ (α-Fe) to a sum of a diffraction intensityD₃₁₁ (Fe₃O₄) and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀))thereof was 0.84.

<Results of Elution Test of the Purifying Iron Composite Particles>

From the results of elution test of the thus obtained iron compositeparticles according to the above evaluation method, it was confirmedthat the iron composite particles exhibited a cadmium elution of lessthan 0.001 mg/L, no detected elution of whole cyanogen, a lead elutionof less than 0.001 mg/L, a chromium elution of less than 0.01 mg/L, anarsenic elution of less than 0.001 mg/L, a whole mercury elution of lessthan 0.0005 mg/L, a selenium elution of less than 0.001 mg/L, a fluorineelution of less than 0.5 mg/L, and a boron elution of less than 1 mg/L.Therefore, it was confirmed that all amounts of these elements elutedwere below the detection limit of the measuring device used, and lowerthan the standard values prescribed in the above Environmental Standard.

Also, the results of the test conducted for measuring contents of therespective elements in the thus obtained iron composite particles areshown in Table 6. As shown in Table 6, it was confirmed that the ironcomposite particles exhibited a cadmium and cadmium compound content ofless than 2 mg/kg; a cyanogen compound content of less than 5 mg/kg; alead and lead compound content of less than 5 mg/kg; a chromium (VI)compound content of less than 5 mg/kg; an arsenic and arsenic compoundcontent of less than 1 mg/kg; a mercury and mercury compound content ofless than 1 mg/kg; a selenium and selenium compound content of less than1 mg/kg; a fluorine and fluorine compound content of less than 20 mg/kg;and a boron and boron compound content of less than 20 mg/kg. Therefore,it was confirmed that all contents of these elements were below thedetection limit of the measuring device used, and lower than thestandard values prescribed in the above Environmental Standard.

<Results of Purification Treatment for Organohalogen Compounds (ApparentReaction Rate Constant)>

According to the above evaluation method, it was confirmed that when thepurifying agent was used in the purification treatment oftrichloroethylene, the apparent reaction rate constant was 0.034 h⁻¹.

Examples 14 to 17 Results of Evaluation of Insolubilization Reaction ofHeavy Metals (Apparent Reaction Rate Constant)

According to the above evaluation method, it was confirmed that when thepurifying agent was used in the purification treatment of heavy metals,the apparent reaction rate constant for arsenic was 0.0195 h⁻¹, theapparent reaction rate constant for chromium was 0.0138 h⁻¹, and theapparent reaction rate constant for lead was 0.0630 h⁻¹.

At this time, the solution used for measuring the residual amounts ofheavy metals was maintained at a pH value of about 10 when adding any ofarsenic, chromium and lead thereto, and the iron composite particlesseparated therefrom still exhibited a black color without any change.Therefore, it was suggested that the a ferrite compound combined withthe heavy metals was formed.

On the contrary, in the case of the reduced iron and electrolytic ironused in the below-mentioned Comparative Examples, the solution used formeasuring the residual amounts of heavy metals had a pH value of about 4when adding chromium thereto, and a pH value of about 6 when adding leadthereto, and the iron particles separated from the solution after addinglead thereto formed a red precipitate. Therefore, it was suggested thatan iron hydroxide compound combined with lead was formed.

<Results of Re-Elution Test for Insolubilized Heavy Metals>

The results of the elution test for insolubilized heavy metals are shownin Table 7. As shown in Table 7, from the results of the alkali elutiontest I, it was confirmed that the amounts of arsenic, chromium and leadeluted were below the Environmental Standard, and from the results ofthe acid elution test I, it was confirmed that the amounts of arsenicand chromium eluted were below the Environmental Standard. If no elutionof heavy metals or the like is detected through these elution tests, itis considered that the insolubilization technique is very effective andprovides a practical and stable treatment, and it is also consideredthat in the case where the insolubilized soil is returned to originalplace, any elution of heavy metals or the like is subsequently no longercaused even when exposed to acid or alkali to some extent.

Meanwhile, in the acid elution test I, only elution of lead wasrecognized. The reason therefor was considered by the present inventorsas follow, though not clearly determined. That is, the iron compositeparticles were added in an amount of 8 g/L and 12 g/L in the arsenic andchromium insolubilization tests, respectively. Whereas, in the leadinsolubilization test, the iron composite particles were added in anamount as small as 1 g/L. The reason why the purification treatment ofcontaminated water was completed notwithstanding the use of such a smallamount of the iron composite particles, was considered to be that a partof lead was absorbed into the iron composite particles in the form of ahydroxide after the insolubilization. However, in the consideration ofre-elution form the particles after the insolubilization, it wassuggested that the use of such a small amount of the iron compositeparticles was inappropriate.

<Goethite Particles>

As goethite particles, there were prepared goethite particles shown inTable 1.

Goethite Particles 1, 2 and 5:

The same procedure as defined in Example 1 was conducted except that theamount of the aqueous Al sulfate solution added was variously changed,thereby obtaining a granulated product of the goethite particles.

Goethite particles 3:

12.8 L of an aqueous ferrous sulfate solution containing Fe²⁺ in anamount of 1.50 mol/L was mixed with 30.2 L of a 0.44-N NaOH aqueoussolution (corresponding to 0.35 equivalent based on Fe²⁺ contained inthe aqueous ferrous sulfate solution), and the obtained mixed solutionwas reacted at a pH of 6.7 and a temperature of 38° C., therebyproducing an aqueous ferrous sulfate solution containing Fe(OH)₂. Then,air was passed through the aqueous ferrous sulfate solution containingFe(OH)₂, at a temperature of 40° C. and a flow rate of 130 L/min for 3.0hours, thereby producing goethite core particles.

The aqueous ferrous sulfate solution containing the goethite coreparticles (in an amount corresponding to 35 mol % based on finallyproduced goethite particles) was mixed with 7.0 L of a 5.4N. Na₂CO₃aqueous solution (corresponding to 1.5 equivalents based on residualFe²⁺ contained in the aqueous ferrous sulfate solution). Then, air waspassed through the mixed solution at a pH of 9.4, a temperature of 42°C. and a flow rate of 130 L/min for 4 hours, thereby producing goethiteparticles. The suspension containing the thus obtained goethiteparticles was mixed with 0.96 L of an aqueous Al sulfate solutioncontaining Al³⁺ in an amount of 0.3 mol/L, fully stirred and then washedwith water using a filter press, thereby obtaining a press cake. Theobtained press cake was extrusion-molded and granulated using acompression-molding machine equipped with a mold plate having an orificediameter of 4 mm, and then dried at 120° C., thereby obtaining agranulated product of the goethite particles.

It was confirmed that the goethite particles constituting the abovegranulated product were acicular particles having an average major axisdiameter of 0.33 μm, an aspect ratio (major axis diameter/minor axisdiameter) of 25.0:1, a BET specific surface area of 70 m²/g, an Alcontent of 0.42% by weight and an S content of 4000 ppm.

Goethite Particles 4:

The same procedure as defined above for production of the goethiteparticles 3 was conducted except that the amount of the aqueous Alsulfate solution added was changed, thereby obtaining a granulatedproduct of the goethite particles.

Examples 2 to 7 and Comparative Examples 1 TO 7 Purifying Iron CompositeParticles and Purifying Agent

The same procedure as defined in Example 1 was conducted except thatkind of goethite particles, heat-dehydrating temperature, addition ornon-addition of sulfuric acid to the suspension containing hematiteparticles as well as amount of the sulfuric acid, if added, andheat-reducing temperature were changed variously, thereby obtainingpurifying iron composite particles and a purifying agent.

Essential production conditions are shown in Table 2, and variousproperties of the obtained purifying iron composite particles andpurifying agent are shown in Table 3.

Meanwhile, in Comparative Example 2, there were used α-Fe-free magnetiteparticles obtained by introducing 100 g of a granulated product of theabove goethite particles 1 into a rotary reducing apparatus, andreducing the granulated product at 300° C. for 180 min while passing H₂gas therethrough until being completely reduced into Fe₃O₄. Further, inComparative Examples 3 and 4, there were used reduced iron particles andelectrolytic iron particles, respectively. Further, in ComparativeExamples 5 and 6, there were used carbonyl iron particles, and inComparative Example 7, there were used sponge iron particles.

Examples 8 to 13 and Comparative Examples 8 to 14 Measurement ofApparent Reaction Rate Constant

The kind of purifying iron composite particles and kind of purifyingagent were changed variously to measure apparent reaction rate constantsthereof. Essential treatment conditions and the measurement results areshown in Table 4.

Meanwhile, in Comparative Examples 12 to 14, since substantially notrichloroethylene was decomposed, the apparent reaction rate constantswere unmeasurable.

Comparative Examples 15 to 18 Measurement of Apparent Reaction RateConstant Upon Insolubilization of Heavy Metals

The kind of purifying iron composite particles and kind of purifyingagent, kind of heavy metals to be insolubilized, and concentrations ofthe heavy metals added were changed variously to measure apparentreaction rate constants thereof. Essential treatment conditions and themeasurement results are shown in Table 5.

Examples 17 to 20

Various properties of the purifying iron composite particles and thepurifying agent after preservation are shown in Table 8. Meanwhile, inExamples 17 to 20, the purifying agent obtained in Example 2 which had asolid content of 30% was preserved in an open system for a period of 1,3, 6 and 12 months, respectively.

Examples 21 to 25 and Comparative Examples 19 and 20 Results ofPurification Treatment of Aliphatic Organohalogen Compounds>

The purification treatment was conducted while variously changing kindof purifying iron composite particles according to the above“preparation of samples for measurement of aliphatic organohalogencompounds” and “evaluation method for aliphatic organohalogencompounds”. The measurement results are shown in Table 9.

Examples 26 to 65

Sodium polyacrylate, sodium hydrogen carbonate and sodium sulfate wereadded to the purifying agent obtained in Examples 3, 5, 6 and 19 whilevariously changing the kind and amount of the sodium polyacrylate, andaddition or non-addition of the sodium hydrogen carbonate and sodiumsulfate, and the amount of the sodium hydrogen carbonate and sodiumsulfate, if added, thereby obtaining purifying agents. The apparentreaction rate constants of the thus obtained purifying agents weremeasured by the same method as defined in Example 1, and the apparentreaction rate constants upon insolubilization of heavy metals weremeasured by the same method as defined in Example 1. The measurementresults are shown in Table 12.

In addition, a travel distance in column as well as penetration time(500 mL) were measured. The measurement results are shown in Table 10.

Examples 26 to 46 and Comparative Examples 21 to 26

The purifying agent obtained in Examples 3, 5, 6 and 19, and ComparativeExamples 2 to 7 was further diluted or mixed with sodium polyacrylate,sodium hydrogen carbonate or sodium sulfate while variously changing thedegree of dilution, kind and amount of sodium polyacrylate added, andaddition or non-addition of sodium hydrogen carbonate or sodium sulfateas well as the amount thereof, if added, as shown in Table 10, therebyobtaining purifying agents.

The additives used were as follows:

Sodium acrylate: “GOOD-RITE K-739” produced by NOVEON CO., LTD.;“JURYMER AC-10NP” produced by NIHON JUNYAKU CO., LTD.; “JURYMER AC-103”produced by NIHON JUNYAKU CO., LTD.; “AQUALIC DL-100” produced by NIPPONSHOKUBAI CO., LTD.

Inorganic salts: sodium hydrogen carbonate produced by KANTO KAGAKU CO.,LTD.; sodium sulfate produced by KANTO KAGAKU CO., LTD.

<Results of Penetrability Test>

The thus obtained purifying agents were subjected to penetrability testusing a sand column. The penetrability of the respective purifyingagents was evaluated as follows. That is, after completion of thepenetration, the sand column was observed to measure a penetrationdistance of the purifying agent from the upper surface of the column, inwhich the soil was colored black as a color of the purifying agent. Theratio of the thus measured penetration distance to a penetrationdistance of the diluted purifying agent containing no additives (Example46) was calculated and determined as a penetrability (penetrationpercentage) of the purifying agent.

In Comparative Examples 21 to 31, the iron particles were immediatelyprecipitated due to coarse particles, and stayed at the upper portion ofthe sand filled in the column, so that substantially no penetration ofthe iron particles into the soil was recognized.

The evaluation results are shown in Table 10.

Meanwhile, when a mixture of the purifying agent and sand was swept offfrom the column after visual observation upon completion of thepenetration, it was confirmed that the black-colored purifying agent wasuniformly dispersed in the sand and, therefore, no banding orsegregation thereof was recognized.

Examples 47 to 65 and Comparative Examples 27 to 28 Results ofPurification Treatment of Organohalogen Compounds (Apparent ReactionRate Constant)

An apparent reaction rate constant of the purifying agent was measuredwhile variously changing the kind of the purifying agent according tothe procedures described in “Preparation of samples for decompositiontest of organohalogen compounds (object to be tested: water) (C)” and“Preparation of samples for decomposition test of organohalogencompounds (object to be tested: soil) (D)”.

Essential treatment conditions and measurement results are shown inTables 12 and 13.

Meanwhile, in Comparative Examples 30 to 32, since substantially nodecomposition of trichloroethylene was caused, the apparent reactionrate constant was unmeasurable.

TABLE 1 Properties of goethite particles Examples and Average majorComparative axis diameter Aspect ratio Examples Shape (μm) (—) GoethiteSpindle-shaped 0.30 12.5:1 particles 1 Goethite Spindle-shaped 0.3012.5:1 particles 2 Goethite Acicular 0.33 25.0:1 particles 3 GoethiteAcicular 0.33 25.0:1 particles 4 Goethite Spindle-shaped 0.30 12.5:1particles 5 Example 1 Spindle-shaped 0.30 12.5:1 Properties of goethiteparticles Examples and BET specific Comparative surface area Al contentS content Examples (m²/g) (wt %) (ppm) Goethite 85 0.13 400 particles 1Goethite 85 0.75 400 particles 2 Goethite 70 0.42 4000 particles 3Goethite 70 0.70 4000 particles 4 Goethite 85 1.50 400 particles 5Example 1 85 0.40 400

TABLE 2 Average particle Heat- diameter of Examples and dehydratinghematite Comparative Kind of goethite temperature particles Examplesparticles used (° C.) (μm) Example 1 — 330 0.24 Example 2 Goethiteparticles 1 300 0.24 Example 3 Goethite particles 1 300 0.24 Example 4Goethite particles 2 350 0.23 Example 5 Goethite particles 3 330 0.25Example 6 Goethite particles 3 260 0.24 Example 7 Goethite particles 4350 0.21 Comparative Goethite particles 5 300 0.21 Example 1 ComparativeGoethite particles 1 300 0.24 Example 2 Amount of Examples and sulfuricReducing Comparative acid added S content temperature Examples (mL/kg)(ppm) (° C.) Condition Example 1 10 3300 450 Iron composite particles &purifying agent Example 2 10 3300 400 Iron composite particles Example 310 3300 450 Purifying agent Example 4 15 4200 500 Purifying agentExample 5 — 4500 400 Iron composite particles Example 6 — 4500 360Purifying agent Example 7 — 4500 500 Purifying agent Comparative 10 3300400 Purifying Example 1 agent Comparative 10 3300 300 Purifying Example2 agent

TABLE 3 Properties of purifying iron composite particles Average BETExamples and particle specific Fe Al S Comparative diameter surfacecontent content content Examples (μm) (m²/g) (wt %) (wt %) (ppm) Example1 0.09 27 83.0 0.67 4000 Example 2 0.07 30 86.1 0.22 4000 Example 3 0.0925 87.2 0.22 4000 Example 4 0.13 11 88.1 1.19 5100 Example 5 0.11 2085.9 0.68 5500 Example 6 0.09 33 76.0 0.68 5500 Example 7 0.16 14 88.81.01 5500 Comparative 0.05 46 71.1 2.40 4000 Example 1 Comparative 0.2452 66.9 0.05 4000 Example 2 Comparative 100 0.05 98.2 0.00 30 Example 3Comparative 50 0.03 98.3 0.00 50 Example 4 Comparative 7.5 0.1 98.8 0.002 Example 5 Comparative 1.65 0.7 99.1 0.00 2 Example 6 Comparative 1800.2 99.0 0.00 3 Example 7 Properties of purifying iron compositeparticles Examples and Crystallite Comparative size Saturationmagnetization value (σs) Examples D₁₁₀ (Å) (Am²/kg) (emu/g) Example 1295 135 135 Example 2 284 142 142 Example 3 292 144 144 Example 4 306146 146 Example 5 298 141 141 Example 6 200 93 93 Example 7 299 149 149Comparative 190 81 81 Example 1 Comparative — 76 76 Example 2Comparative 440 204 204 Example 3 Comparative 430 208 208 Example 4Comparative 256 208 208 Example 5 Comparative 93 203 203 Example 6Comparative 221 197 197 Example 7 Properties of purifying iron compositeparticles X-ray diffraction Examples and intensity ratio ComparativeD₁₁₀/(D₁₁₀ + D₃₁₁) Examples Crystal phase (-) Condition Example 1 α-Feand Fe₃O₄ 0.84 Iron composite mixed phase particles & purifying agentExample 2 α-Fe and Fe₃O₄ 0.88 Iron composite mixed phase particlesExample 3 α-Fe and Fe₃O₄ 0.90 Purifying agent mixed phase Example 4 α-Feand Fe₃O₄ 0.92 Purifying agent mixed phase Example 5 α-Fe and Fe₃O₄ 0.88Iron composite mixed phase particles Example 6 α-Fe and Fe₃O₄ 0.35Purifying agent mixed phase Example 7 α-Fe and Fe₃O₄ 0.94 Purifyingagent mixed phase Comparative α-Fe and Fe₃O₄ 0.14 Purifying agentExample 1 mixed phase Comparative Fe₃O₄ single — Particles Example 2phase Comparative α-Fe single 1.00 Particles Example 3 phase Comparativeα-Fe single 1.00 Particles Example 4 phase Comparative α-Fe single 1.00Particles Example 5 phase Comparative α-Fe single 1.00 Particles Example6 phase Comparative α-Fe single 1.00 Particles Example 7 phase

TABLE 4 Apparent reaction Examples and Kind of iron composite rateconstant Comparative particles or purifying Kobs Examples agent used(h⁻¹) Example 1 — 0.0340 Example 8 Example 2 0.0310 Example 9 Example 30.0330 Example 10 Example 4 0.0270 Example 11 Example 5 0.0260 Example12 Example 6 0.0240 Example 13 Example 7 0.0350 Comparative ComparativeExample 1 0.0048 Example 8 Comparative Comparative Example 2 0.0010Example 9 Comparative Comparative Example 3 0.0007 Example 10Comparative Comparative Example 4 0.0009 Example 11 ComparativeComparative Example 5 Undecomposable Example 12 Comparative ComparativeExample 6 Undecomposable Example 13 Comparative Comparative Example 7Undecomposable Example 14

TABLE 5 Kind of iron Apparent composite reaction rate Examples andparticles or constant Comparative purifying agent Kind of heavy KobsExamples used metals added (h⁻¹) Example 14 Example 1 As 0.0195 Example15 Example 1 Cr 0.0138 Example 16 Example 1 Pb 0.0630 ComparativeComparative Cr 0.0003 Example 15 Example 3 Comparative Comparative Pb0.0339 Example 16 Example 3 Comparative Comparative Cr 0.0003 Example 17Example 4 Comparative Comparative Pb 0.0282 Example 18 Example 4

TABLE 6 Iron composite Environmental particles Analyzed standard Testingused Compound value value method Example 1 Cadmium <2 mg/kg ≦150 mg/kgJIS K0102 and 55.1 cadmium compound Example 1 Cyanogen <5 mg/kg  ≦50mg/kg JIS K0102 compound 38.1 & 38.3 Example 1 Lead and <5 mg/kg ≦150mg/kg JIS K0102 lead 54.1 compound Example 1 Chromium <5 mg/kg ≦250mg/kg JIS K0102 (VI) 65.2.1 compound Example 1 Arsenic and <1 mg/kg ≦150mg/kg JIS K0102 arsenic 61.2 compound Example 1 Mercury and <1 mg/kg ≦15 mg/kg Attached mercury Table 1 of compound Sho-46 Notification No.59 of Environmental Agency Example 1 Selenium <1 mg/kg ≦150 mg/kg JISK0102 and 67.2 selenium compound Example 1 Fluorine <20 mg/kg  ≦4000mg/kg  JIS K0102 and 34.1 fluorine compound Example 1 Boron and <20mg/kg  ≦4000 mg/kg  JIS K0102 boron 47.3 compound

TABLE 7 Iron Environ- composite mental particles Analyzed standard usedCompound value value Testing method Example 1 Arsenic <0.001 mg/L <0.01mg/L Acid-addition elution testing method I: JIS K0102 61.2 Example 1Arsenic <0.001 mg/L <0.01 mg/L Alkali-addition elution testing method I:JIS K0102 61.2 Example 1 Whole <0.05 mg/L Cr⁶⁺ Acid-addition chromium<0.05 mg/L elution testing method I: JIS K0102 61.2 Example 1 Whole<0.05 mg/L Cr⁶⁺ Alkali-addition chromium <0.05 mg/L elution testingmethod I: JIS K0102 61.2 Example 1 Lead 5.5 mg/L <0.01 mg/LAcid-addition elution testing method I: JIS K0102 61.2 Example 1 Lead<0.005 mg/L <0.01 mg/L Alkali-addition elution testing method I: JISK0102 61.2

TABLE 8 Properties of purifying iron composite particles PreservationDiameter period of of coarse BET purifying particles specific Fe agentproduced surface content Examples (days) (μm) (m²/g) (wt %) Example 1730 0.20 27 77.5 Example 18 90 0.50 20 73.8 Example 19 180 1.10 21 71.2Example 20 360 3.00 20 69.8 Properties of purifying iron compositeparticles Crystallite Saturation magnetization size D₁₁₀ value (σs)Examples (Å) (Am²/kg) (emu/g) Example 17 273 121 121 Example 18 273 9797 Example 19 264 87 87 Example 20 265 88 88 Properties of purifyingiron composite particles X-ray diffraction intensity ratio D₁₁₀/(D₁₁₀ +D₃₁₁) Examples Crystal phase (—) Condition Example 17 α-Fe and Fe₃O₄0.71 Purifying agent mixed phase Example 18 α-Fe and Fe₃O₄ 0.45Purifying agent mixed phase Example 19 α-Fe and Fe₃O₄ 0.24 Purifyingagent mixed phase Example 20 α-Fe and Fe₃O₄ 0.25 Purifying agent mixedphase

TABLE 9 Examples and Kind of iron Residual percentage Comparativecomposite of trichloroethylene Examples particles used (%) Example 21Example 2 2.7 Example 22 Example 17 5.1 Example 23 Example 18 5.8Example 24 Example 19 8.1 Example 25 Example 20 7.9 ComparativeComparative 70.0 Example 19 Example 3 Comparative Comparative 71.0Example 20 Example 4

TABLE 10 Solid content of Sodium polyacrylate Kind of iron compositeSolid purifying particles content Examples agent (g/L) Kind (g/L)Example 26 Example 3 8.0 K-739 1.3 Example 27 Example 3 8.0 DL-100 1.3Example 28 Example 3 8.0 AC-103 1.3 Example 29 Example 3 8.0 — — Example30 Example 3 8.0 — — Example 31 Example 3 8.0 — — Example 32 Example 38.0 AC-10NP 0.8 Example 33 Example 3 3.3 AC-10NP 0.6 Example 34 Example3 8.0 AC-10NP 1.3 Example 35 Example 5 8.0 AC-10NP 1.3 Example 36Example 6 8.0 AC-10NP 1.3 Example 37 Example 3 70 AC-10NP 11.7  Example38 Example 19 8.0 AC-10NP 1.3 Example 39 Example 3 8.0 AC-10NP 8.0Example 40 Example 3 8.0 AC-10NP 1.3 Example 41 Example 3 8.0 AC-10NP1.3 Example 42 Example 3 8.0 AC-10NP 1.3 Example 43 Example 3 8.0AC-10NP 1.3 Example 44 Example 3 8.0 AC-10NP 1.3 Example 45 Example 38.0 AC-10NP 1.3 Example 46 Example 3 8.0 — — Content of Content ofPenetration NaHCO₃ Na₂SO₄ percentage Examples (wt %) (wt %) (%) Example26 — — 450 Example 27 — — 460 Example 28 — — 460 Example 29 0.06 0.42210 Example 30 0.15 — 220 Example 31 — 0.91 210 Example 32 — — 220Example 33 — — 280 Example 34 — — 460 Example 35 — — 450 Example 36 — —460 Example 37 — — 440 Example 38 — — 410 Example 39 — — 500 Example 400.02 0.22 520 Example 41 0.06 0.42 700 Example 42 0.06 — 510 Example 430.15 — 690 Example 44 — 0.23 520 Example 45 — 0.91 690 Example 46 — —100

TABLE 11 Solid content of Sodium polyacrylate Kind of iron compositeSolid Comparative purifying particles content Examples agent (g/L) Kind(g/L) Comparative Comparative 8.0 AC-10NP 1.3 Example 21 Example 2Comparative Comparative 8.0 AC-10NP 1.3 Example 22 Example 3 ComparativeComparative 8.0 AC-10NP 1.3 Example 23 Example 4 Comparative Comparative8.0 AC-10NP 1.3 Example 24 Example 5 Comparative Comparative 8.0 AC-10NP1.3 Example 25 Example 6 Comparative Comparative 8.0 AC-10NP 1.3 Example26 Example 7 Content of Content of Penetration NaHCO₃ Na₂SO₄ percentageExamples (wt %) (wt %) (%) Comparative — — 20 Example 21 Comparative — —10 Example 22 Comparative — — 10 Example 23 Comparative — — 10 Example24 Comparative — — 10 Example 25 Comparative — — 10 Example 26

TABLE 12 Solid content of Sodium polyacrylate Kind of iron compositeSolid purifying particles content Examples agent (g/L) Kind (g/L)Example 47 Example 3 2.0 K-739 0.3 Example 48 Example 3 2.0 DL-100 0.3Example 49 Example 3 2.0 AC-103 0.3 Example 50 Example 3 2.0 — — Example51 Example 3 2.0 — — Example 52 Example 3 2.0 — — Example 53 Example 32.0 AC-10NP 0.2 Example 54 Example 3 2.0 AC-10NP 0.3 Example 55 Example5 2.0 AC-10NP 0.3 Example 56 Example 6 2.0 AC-10NP 0.3 Example 57Example 19 2.0 AC-10NP 0.3 Example 58 Example 3 2.0 AC-10NP 2.0 Example59 Example 3 2.0 AC-10NP 0.3 Example 60 Example 3 2.0 AC-10NP 0.3Example 61 Example 3 2.0 AC-10NP 0.3 Example 62 Example 3 2.0 AC-10NP0.3 Example 63 Example 3 2.0 AC-10NP 0.3 Example 64 Example 3 2.0AC-10NP 0.3 Example 65 Example 3 2.0 — — Content of Content of Kobs KobsNaHCO₃ Na₂SO₄ Soil Water Examples (wt %) (wt %) (1/h) (1/h) Example 47 —— 0.0141 0.0153 Example 48 — — 0.0148 0.0159 Example 49 — — 0.01450.0155 Example 50 0.06 0.42 0.0161 0.0175 Example 51 0.15 — 0.01520.0170 Example 52 — 0.91 0.0166 0.0180 Example 53 — — 0.0148 0.0165Example 54 — — 0.0142 0.0157 Example 55 — — 0.0127 0.0138 Example 56 — —0.0145 0.0160 Example 57 — — 0.0119 0.0105 Example 58 — — 0.0129 0.0140Example 59 0.02 0.22 0.0137 0.0151 Example 60 0.06 0.42 0.0138 0.0148Example 61 0.06 — 0.0140 0.0147 Example 62 0.15 — 0.0132 0.0144 Example63 — 0.23 0.0142 0.0152 Example 64 — 0.91 0.0138 0.0150 Example 65 — —0.0180 0.0188

TABLE 13 Solid content of Sodium polyacrylate Kind of iron compositeSolid Comparative purifying particles content Examples agent (g/L) Kind(g/L) Comparative Comparative 2.0 AC-10NP 0.3 Example 27 Example 2Comparative Comparative 2.0 AC-10NP 0.3 Example 28 Example 3 ComparativeComparative 2.0 AC-10NP 0.3 Example 29 Example 4 Comparative Comparative2.0 AC-10NP 0.3 Example 30 Example 5 Comparative Comparative 2.0 AC-10NP0.3 Example 31 Example 6 Comparative Comparative 2.0 AC-10NP 0.3 Example32 Example 7 Content Content of of Kobs Kobs Comparative NaHCO₃ Na₂SO₄Soil Water Examples (wt %) (wt %) (1/h) (1/h) Comparative — — 0.00070.0010 Example 27 Comparative — — 0.0006 0.0007 Example 28 Comparative —— 0.0008 0.0009 Example 29 Comparative — — Undecomposable UndecomposableExample 30 Comparative — — Undecomposable Undecomposable Example 31Comparative — — Undecomposable Undecomposable Example 32

1.-18. (canceled)
 19. A method for purifying soil or ground water,comprising: mixing and contacting the iron composite particlescomprising α-Fe and magnetite, and having a ratio of a diffractionintensity D₁₁₀ of (100) plane of α-Fe to a sum of a diffractionintensity D₃₁₁ of (311) plane of magnetite and the diffraction intensityD₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.30 to 0.95 as measured from X-raydiffraction spectrum of the iron composite particles an Al content of0.10 to 1.50% by weight and an S content of 3500 to 7000 ppm with soilor ground water, which are contaminated with organohalogen compounds,heavy metals or the like, or both thereof.
 20. A method for purifyingsoil or ground water, comprising: mixing and contacting the ironcomposite particles comprising a water suspension containing ironcomposite particles as an effective ingredient which comprise α-Fe andmagnetite and have a ratio of a diffraction intensity D₁₁₀ of (110)plane of α-Fe to a sum of a diffraction intensity D₃₁₁ of (311) plane ofmagnetite and the diffraction intensity D₁₁₀ (D₁₁₀/(D₃₁₁+D₁₁₀)) of 0.20to 0.95 as measured from X-ray diffraction spectrum of the ironcomposite particles, an Al content of 0.10 to 1.50% by weight, an Scontent of 3500 to 7000 ppm, an average particle diameter of 0.05 to 0.5μm and a particle diameter of coarse particles of usually 0.5 to 5.0 μmwith soil or ground water, which are contaminated with organohalogencompounds, heavy metals or the like, or both thereof.
 21. A method forpurifying soil or ground water, comprising: comprising a watersuspension containing iron composite particles as an effectiveingredient which comprise α-Fe and magnetite, and have a ratio of adiffraction intensity D₁₁₀ of (110) plane of α-Fe to a sum of adiffraction intensity D₃₁₁ of (311) plane of magnetite and thediffraction intensity D₁₁₀ (D₁₀₀/(D₃₁₁+D₁₁₀)) of 0.20 to 0.95 asmeasured from X-ray diffraction spectrum of the iron compositeparticles, an Al content of 0.10 to 1.50% by weight, an S content of atleast 3500 ppm, a saturation magnetization value of 60 to 155 μm²/kg, acrystallite size of (110) plane of α-Fe of 200 to 400 Å, an Fe contentof not less than 65% by weight based on the weight of whole particles,an average particle diameter of 0.05 to 0.5 μm and a particle diameterof coarse particles of usually 0.5 to 5.0 μm, mixing and contacting theiron composite particles as defined in claim 7 with soil or groundwater, which are contaminated with organohalogen compounds, heavy metalsor the like, or both thereof.